diff --git src/js/_enqueues/vendor/plupload/handlers.js src/js/_enqueues/vendor/plupload/handlers.js
index c7e3c253d3..fa602daf43 100644
--- src/js/_enqueues/vendor/plupload/handlers.js
+++ src/js/_enqueues/vendor/plupload/handlers.js
@@ -486,7 +486,7 @@ jQuery( document ).ready( function( $ ) {
 
 		times = tryAgainCount[ file.id ];
 
-		if ( times && times > 8 ) {
+		if ( times && times > 4 ) {
 			/*
 			 * The file may have been uploaded and attachment post created,
 			 * but post-processing and resizing failed...
diff --git src/js/_enqueues/vendor/plupload/wp-plupload.js src/js/_enqueues/vendor/plupload/wp-plupload.js
index 217b3c09e2..0fdebf77d1 100644
--- src/js/_enqueues/vendor/plupload/wp-plupload.js
+++ src/js/_enqueues/vendor/plupload/wp-plupload.js
@@ -138,7 +138,7 @@ window.wp = window.wp || {};
 
 			times = tryAgainCount[ file.id ];
 
-			if ( times && times > 8 ) {
+			if ( times && times > 4 ) {
 				/*
 				 * The file may have been uploaded and attachment post created,
 				 * but post-processing and resizing failed...
diff --git src/wp-admin/includes/image.php src/wp-admin/includes/image.php
index b0cffc504f..f937bdc2ff 100644
--- src/wp-admin/includes/image.php
+++ src/wp-admin/includes/image.php
@@ -71,29 +71,22 @@ function wp_crop_image( $src, $src_x, $src_y, $src_w, $src_h, $dst_w, $dst_h, $s
 }
 
 /**
- * Compares the existing image sub-sizes (as saved in the attachment meta)
- * to the currently registered image sub-sizes, and returns the difference.
+ * Compare the existing image sub-sizes (as saved in the attachment meta)
+ * to the currently registered image sub-sizes, and return the difference.
  *
  * Registered sub-sizes that are larger than the image are skipped.
  *
  * @since 5.3.0
- * @since 6.1.0 The $mime_type parameter was added.
  *
- * @param int    $attachment_id The image attachment post ID.
- * @param string $mime_type     Optional. The mime type to check for missing sizes. Default is the primary image mime.
+ * @param int $attachment_id The image attachment post ID.
  * @return array[] Associative array of arrays of image sub-size information for
  *                 missing image sizes, keyed by image size name.
  */
-function wp_get_missing_image_subsizes( $attachment_id, $mime_type = '' ) {
+function wp_get_missing_image_subsizes( $attachment_id ) {
 	if ( ! wp_attachment_is_image( $attachment_id ) ) {
 		return array();
 	}
 
-	$primary_mime_type = get_post_mime_type( get_post( $attachment_id ) );
-	if ( ! $mime_type ) {
-		$mime_type = $primary_mime_type;
-	}
-
 	$registered_sizes = wp_get_registered_image_subsizes();
 	$image_meta       = wp_get_attachment_metadata( $attachment_id );
 
@@ -136,38 +129,19 @@ function wp_get_missing_image_subsizes( $attachment_id, $mime_type = '' ) {
 	 * However we keep the old sub-sizes with the previous dimensions
 	 * as the image may have been used in an older post.
 	 */
-	$missing_sizes = array();
-	foreach ( $possible_sizes as $size_name => $size_data ) {
-		if ( ! isset( $image_meta['sizes'][ $size_name ] ) ) {
-			$missing_sizes[ $size_name ] = $size_data;
-			continue;
-		}
-
-		if ( ( isset( $size_data['mime-type'] ) && $size_data['mime-type'] === $mime_type ) || isset( $size_data['sources'][ $mime_type ] ) ) {
-			continue;
-		}
-
-		$missing_sizes[ $size_name ] = $size_data;
-	}
-
-	// Filter secondary mime types to those sizes that are enabled.
-	if ( $primary_mime_type !== $mime_type ) {
-		$missing_sizes = _wp_filter_image_sizes_additional_mime_type_support( $missing_sizes, $attachment_id );
-	}
+	$missing_sizes = array_diff_key( $possible_sizes, $image_meta['sizes'] );
 
 	/**
 	 * Filters the array of missing image sub-sizes for an uploaded image.
 	 *
 	 * @since 5.3.0
-	 * @since 6.1.0 The $mime_type filter parameter was added.
 	 *
 	 * @param array[] $missing_sizes Associative array of arrays of image sub-size information for
 	 *                               missing image sizes, keyed by image size name.
 	 * @param array   $image_meta    The image meta data.
 	 * @param int     $attachment_id The image attachment post ID.
-	 * @param string  $mime_type     The image mime type to get missing sizes for.
 	 */
-	return apply_filters( 'wp_get_missing_image_subsizes', $missing_sizes, $image_meta, $attachment_id, $mime_type );
+	return apply_filters( 'wp_get_missing_image_subsizes', $missing_sizes, $image_meta, $attachment_id );
 }
 
 /**
@@ -175,7 +149,6 @@ function wp_get_missing_image_subsizes( $attachment_id, $mime_type = '' ) {
  * create them and update the image meta data.
  *
  * @since 5.3.0
- * @since 6.1.0 Now supports additional mime types, creating the additional sub-sizes and 'full' sized images.
  *
  * @param int $attachment_id The image attachment post ID.
  * @return array|WP_Error The updated image meta data array or WP_Error object
@@ -194,33 +167,14 @@ function wp_update_image_subsizes( $attachment_id ) {
 			return new WP_Error( 'invalid_attachment', __( 'The attached file cannot be found.' ) );
 		}
 	} else {
-		// Get the primary and additional mime types to generate.
-		list( $primary_mime_type, $additional_mime_types ) = _wp_get_primary_and_additional_mime_types( $image_file, $attachment_id );
+		$missing_sizes = wp_get_missing_image_subsizes( $attachment_id );
 
-		// Generate missing 'full' image files for additional mime types.
-		if ( ! empty( $additional_mime_types ) ) {
-			if ( isset( $image_meta['sources'] ) ) {
-				$missing_mime_types = array_diff( $additional_mime_types, array_keys( $image_meta['sources'] ) );
-			} else {
-				$missing_mime_types = $additional_mime_types;
-			}
-			if ( ! empty( $missing_mime_types ) ) {
-				$image_meta = _wp_make_additional_mime_types( $missing_mime_types, $image_file, $image_meta, $attachment_id );
-			}
+		if ( empty( $missing_sizes ) ) {
+			return $image_meta;
 		}
 
-		// Generate missing image sub-sizes for each mime type.
-		$all_mime_types = array_merge( array( $primary_mime_type ), $additional_mime_types );
-		foreach ( $all_mime_types as $mime_type ) {
-			$missing_sizes = wp_get_missing_image_subsizes( $attachment_id, $mime_type );
-
-			if ( empty( $missing_sizes ) ) {
-				continue;
-			}
-
-			// This also updates the image meta.
-			$image_meta = _wp_make_subsizes( $missing_sizes, $image_file, $image_meta, $attachment_id, $mime_type );
-		}
+		// This also updates the image meta.
+		$image_meta = _wp_make_subsizes( $missing_sizes, $image_file, $image_meta, $attachment_id );
 	}
 
 	/** This filter is documented in wp-admin/includes/image.php */
@@ -268,13 +222,12 @@ function _wp_image_meta_replace_original( $saved_data, $original_file, $image_me
 }
 
 /**
- * Creates image mime variations and sub-sizes, adds the new data to the image meta `sizes` array, and updates the image metadata.
+ * Creates image sub-sizes, adds the new data to the image meta `sizes` array, and updates the image metadata.
  *
  * Intended for use after an image is uploaded. Saves/updates the image metadata after each
  * sub-size is created. If there was an error, it is added to the returned image metadata array.
  *
  * @since 5.3.0
- * @since 6.1.0 Generates sub-sizes in alternate mime types based on the `wp_image_mime_transforms` filter.
  *
  * @param string $file          Full path to the image file.
  * @param int    $attachment_id Attachment ID to process.
@@ -295,7 +248,6 @@ function wp_create_image_subsizes( $file, $attachment_id ) {
 		'file'     => _wp_relative_upload_path( $file ),
 		'filesize' => wp_filesize( $file ),
 		'sizes'    => array(),
-		'sources'  => array(),
 	);
 
 	// Fetch additional metadata from EXIF/IPTC.
@@ -305,127 +257,9 @@ function wp_create_image_subsizes( $file, $attachment_id ) {
 		$image_meta['image_meta'] = $exif_meta;
 	}
 
-	// Get the primary and additional mime types to generate.
-	list( $primary_mime_type, $additional_mime_types ) = _wp_get_primary_and_additional_mime_types( $file, $attachment_id );
-
-	list( $editor, $resized, $rotated ) = _wp_maybe_scale_and_rotate_image( $file, $attachment_id, $imagesize, $exif_meta, $primary_mime_type );
-	if ( is_wp_error( $editor ) ) {
-		return $image_meta;
-	}
-	$suffix = _wp_get_image_suffix( $resized, $rotated );
-
-	// Save image only if either it was modified or if the primary mime type is different from the original.
-	if ( ! empty( $suffix ) || $primary_mime_type !== $imagesize['mime'] ) {
-		$saved = $editor->save( $editor->generate_filename( $suffix ) );
-
-		if ( ! is_wp_error( $saved ) ) {
-			$image_meta = _wp_image_meta_replace_original( $saved, $file, $image_meta, $attachment_id );
-
-			// If the image was rotated update the stored EXIF data.
-			if ( true === $rotated && ! empty( $image_meta['image_meta']['orientation'] ) ) {
-				$image_meta['image_meta']['orientation'] = 1;
-			}
-		} else {
-			// TODO: Log errors.
-		}
-	}
-
-	// Set 'sources' for the primary mime type.
-	$image_meta['sources'][ $primary_mime_type ] = _wp_get_sources_from_meta( $image_meta );
-
-	/*
-	 * Initial save of the new metadata.
-	 * At this point the file was uploaded and moved to the uploads directory
-	 * but the image sub-sizes haven't been created yet and the `sizes` array is empty.
-	 */
-	wp_update_attachment_metadata( $attachment_id, $image_meta );
-
-	if ( ! empty( $additional_mime_types ) ) {
-		// Use the original file's exif_meta orientation and size information for secondary mime generation to ensure
-		// sub-sized images are correctly scaled and rotated.
-
-		// Save data.
-		$saved_meta                = array();
-		$saved_meta['orientation'] = $image_meta['image_meta']['orientation'];
-		$saved_meta['width']       = $image_meta['width'];
-		$saved_meta['height']      = $image_meta['height'];
-
-		// Temporarily set the image meta to the original file's meta.
-		$image_meta['image_meta']['orientation'] = $exif_meta['orientation'];
-		$image_meta['width']                     = $imagesize[0];
-		$image_meta['height']                    = $imagesize[1];
-
-		$image_meta = _wp_make_additional_mime_types( $additional_mime_types, $file, $image_meta, $attachment_id );
-
-		// Restore the saved meta data.
-		$image_meta['image_meta']['orientation'] = $saved_meta['orientation'];
-		$image_meta['width']                     = $saved_meta['width'];
-		$image_meta['height']                    = $saved_meta['height'];
-
-	}
-
-	$new_sizes = wp_get_registered_image_subsizes();
-
-	/**
-	 * Filters the image sizes automatically generated when uploading an image.
-	 *
-	 * @since 2.9.0
-	 * @since 4.4.0 Added the `$image_meta` argument.
-	 * @since 5.3.0 Added the `$attachment_id` argument.
-	 *
-	 * @param array $new_sizes     Associative array of image sizes to be created.
-	 * @param array $image_meta    The image meta data: width, height, file, sizes, etc.
-	 * @param int   $attachment_id The attachment post ID for the image.
-	 */
-	$new_sizes = apply_filters( 'intermediate_image_sizes_advanced', $new_sizes, $image_meta, $attachment_id );
-
-	$image_meta = _wp_make_subsizes( $new_sizes, $file, $image_meta, $attachment_id, $primary_mime_type );
-
-	// Filter secondary mime types to those sizes that are enabled.
-	$new_sizes = _wp_filter_image_sizes_additional_mime_type_support( $new_sizes, $attachment_id );
-
-	foreach ( $additional_mime_types as $additional_mime_type ) {
-		$image_meta = _wp_make_subsizes( $new_sizes, $file, $image_meta, $attachment_id, $additional_mime_type );
-	}
-
-	return $image_meta;
-}
-
-/**
- * Returns a WP_Image_Editor instance where the image file has been scaled and rotated as necessary.
- *
- * @since 6.1.0
- * @access private
- *
- * @param string     $file          Full path to the image file.
- * @param int        $attachment_id Attachment ID.
- * @param array      $imagesize     {
- *     Indexed array of the image width and height in pixels.
- *
- *     @type int $0 The image width.
- *     @type int $1 The image height.
- * }
- * @param array|null $exif_meta EXIF metadata if extracted from the image file.
- * @param string     $mime_type Output mime type.
- * @return array Array with three entries: The WP_Image_Editor instance, whether the image was resized, and whether the
- *               image was rotated (booleans). Each entry can alternatively be a WP_Error in case something went wrong.
- */
-function _wp_maybe_scale_and_rotate_image( $file, $attachment_id, $imagesize, $exif_meta, $mime_type ) {
-	$resized = false;
-	$rotated = false;
-
-	$editor = wp_get_image_editor( $file, array( 'mime_type' => $mime_type ) );
-	if ( is_wp_error( $editor ) ) {
-		// This image cannot be edited.
-		return array( $editor, $resized, $rotated );
-	}
-
-	if ( ! empty( $mime_type ) ) {
-		$editor->set_output_mime_type( $mime_type );
-	}
-
 	// Do not scale (large) PNG images. May result in sub-sizes that have greater file size than the original. See #48736.
-	if ( 'image/png' !== $mime_type ) {
+	if ( 'image/png' !== $imagesize['mime'] ) {
+
 		/**
 		 * Filters the "BIG image" threshold value.
 		 *
@@ -451,65 +285,96 @@ function _wp_maybe_scale_and_rotate_image( $file, $attachment_id, $imagesize, $e
 
 		// If the original image's dimensions are over the threshold,
 		// scale the image and use it as the "full" size.
-		if ( $threshold && ( $imagesize[0] > $threshold || $imagesize[1] > $threshold ) ) {
+		if ( $threshold && ( $image_meta['width'] > $threshold || $image_meta['height'] > $threshold ) ) {
+			$editor = wp_get_image_editor( $file );
+
+			if ( is_wp_error( $editor ) ) {
+				// This image cannot be edited.
+				return $image_meta;
+			}
+
 			// Resize the image.
 			$resized = $editor->resize( $threshold, $threshold );
+			$rotated = null;
 
 			// If there is EXIF data, rotate according to EXIF Orientation.
 			if ( ! is_wp_error( $resized ) && is_array( $exif_meta ) ) {
-				$rotated = $editor->maybe_exif_rotate();
+				$resized = $editor->maybe_exif_rotate();
+				$rotated = $resized;
+			}
+
+			if ( ! is_wp_error( $resized ) ) {
+				// Append "-scaled" to the image file name. It will look like "my_image-scaled.jpg".
+				// This doesn't affect the sub-sizes names as they are generated from the original image (for best quality).
+				$saved = $editor->save( $editor->generate_filename( 'scaled' ) );
+
+				if ( ! is_wp_error( $saved ) ) {
+					$image_meta = _wp_image_meta_replace_original( $saved, $file, $image_meta, $attachment_id );
+
+					// If the image was rotated update the stored EXIF data.
+					if ( true === $rotated && ! empty( $image_meta['image_meta']['orientation'] ) ) {
+						$image_meta['image_meta']['orientation'] = 1;
+					}
+				} else {
+					// TODO: Log errors.
+				}
+			} else {
+				// TODO: Log errors.
 			}
 		} elseif ( ! empty( $exif_meta['orientation'] ) && 1 !== (int) $exif_meta['orientation'] ) {
 			// Rotate the whole original image if there is EXIF data and "orientation" is not 1.
+
+			$editor = wp_get_image_editor( $file );
+
+			if ( is_wp_error( $editor ) ) {
+				// This image cannot be edited.
+				return $image_meta;
+			}
+
+			// Rotate the image.
 			$rotated = $editor->maybe_exif_rotate();
-		}
-	}
 
-	return array( $editor, $resized, $rotated );
-}
+			if ( true === $rotated ) {
+				// Append `-rotated` to the image file name.
+				$saved = $editor->save( $editor->generate_filename( 'rotated' ) );
 
-/**
- * Gets the suffix to use for image files based on resizing and rotating.
- *
- * @since 6.1.0
- * @access private
- *
- * @param bool|WP_Error Whether the image was resized, or an error if resizing failed.
- * @param bool|WP_Error Whether the image was rotated, or an error if rotating failed.
- * @return string The suffix to use for the file name, or empty string if none.
- */
-function _wp_get_image_suffix( $resized, $rotated ) {
-	if ( $resized && ! is_wp_error( $resized ) ) {
-		// Append "-scaled" to the image file name. It will look like "my_image-scaled.jpg".
-		// This doesn't affect the sub-sizes names as they are generated from the original image (for best quality).
-		return 'scaled';
-	}
+				if ( ! is_wp_error( $saved ) ) {
+					$image_meta = _wp_image_meta_replace_original( $saved, $file, $image_meta, $attachment_id );
 
-	if ( true === $rotated ) {
-		// Append `-rotated` to the image file name.
-		return 'rotated';
+					// Update the stored EXIF data.
+					if ( ! empty( $image_meta['image_meta']['orientation'] ) ) {
+						$image_meta['image_meta']['orientation'] = 1;
+					}
+				} else {
+					// TODO: Log errors.
+				}
+			}
+		}
 	}
 
-	if ( is_wp_error( $resized ) || is_wp_error( $rotated ) ) {
-		// TODO: Log errors.
-	}
-	return '';
-}
+	/*
+	 * Initial save of the new metadata.
+	 * At this point the file was uploaded and moved to the uploads directory
+	 * but the image sub-sizes haven't been created yet and the `sizes` array is empty.
+	 */
+	wp_update_attachment_metadata( $attachment_id, $image_meta );
 
-/**
- * Gets a sources array element from a meta.
- *
- * @since 6.1.0
- * @access private
- *
- * @param array $meta The meta to get the source from.
- * @return array The source array element.
- */
-function _wp_get_sources_from_meta( $meta ) {
-	return array(
-		'file'     => isset( $meta['file'] ) ? wp_basename( $meta['file'] ) : '',
-		'filesize' => isset( $meta['filesize'] ) ? $meta['filesize'] : wp_filesize( $meta['path'] ),
-	);
+	$new_sizes = wp_get_registered_image_subsizes();
+
+	/**
+	 * Filters the image sizes automatically generated when uploading an image.
+	 *
+	 * @since 2.9.0
+	 * @since 4.4.0 Added the `$image_meta` argument.
+	 * @since 5.3.0 Added the `$attachment_id` argument.
+	 *
+	 * @param array $new_sizes     Associative array of image sizes to be created.
+	 * @param array $image_meta    The image meta data: width, height, file, sizes, etc.
+	 * @param int   $attachment_id The attachment post ID for the image.
+	 */
+	$new_sizes = apply_filters( 'intermediate_image_sizes_advanced', $new_sizes, $image_meta, $attachment_id );
+
+	return _wp_make_subsizes( $new_sizes, $file, $image_meta, $attachment_id );
 }
 
 /**
@@ -519,26 +384,20 @@ function _wp_get_sources_from_meta( $meta ) {
  * Errors are stored in the returned image metadata array.
  *
  * @since 5.3.0
- * @since 6.1.0 The $mime_type parameter was added.
  * @access private
  *
- * @param array  $new_sizes       Array defining what sizes to create.
- * @param string $file            Full path to the image file.
- * @param array  $image_meta      The attachment meta data array.
- * @param int    $attachment_id   Attachment ID to process.
- * @param string $mime_type       Optional. The mime type to check for missing sizes. Default is the image mime of $file.
+ * @param array  $new_sizes     Array defining what sizes to create.
+ * @param string $file          Full path to the image file.
+ * @param array  $image_meta    The attachment meta data array.
+ * @param int    $attachment_id Attachment ID to process.
  * @return array The attachment meta data with updated `sizes` array. Includes an array of errors encountered while resizing.
  */
-function _wp_make_subsizes( $new_sizes, $file, $image_meta, $attachment_id, $mime_type = '' ) {
+function _wp_make_subsizes( $new_sizes, $file, $image_meta, $attachment_id ) {
 	if ( empty( $image_meta ) || ! is_array( $image_meta ) ) {
 		// Not an image attachment.
 		return array();
 	}
 
-	if ( ! $mime_type ) {
-		$mime_type = wp_get_image_mime( $file );
-	}
-
 	// Check if any of the new sizes already exist.
 	if ( isset( $image_meta['sizes'] ) && is_array( $image_meta['sizes'] ) ) {
 		foreach ( $image_meta['sizes'] as $size_name => $size_meta ) {
@@ -548,11 +407,7 @@ function _wp_make_subsizes( $new_sizes, $file, $image_meta, $attachment_id, $mim
 			 * To change the behavior, unset changed/mismatched sizes in the `sizes` array in image meta.
 			 */
 			if ( array_key_exists( $size_name, $new_sizes ) ) {
-				// Unset the size if it is either the required mime type already exists either as main mime type or
-				// within sources.
-				if ( $size_meta['mime-type'] === $mime_type || isset( $size_meta['sources'][ $mime_type ] ) ) {
-					unset( $new_sizes[ $size_name ] );
-				}
+				unset( $new_sizes[ $size_name ] );
 			}
 		}
 	} else {
@@ -578,15 +433,13 @@ function _wp_make_subsizes( $new_sizes, $file, $image_meta, $attachment_id, $mim
 
 	$new_sizes = array_filter( array_merge( $priority, $new_sizes ) );
 
-	$editor = wp_get_image_editor( $file, array( 'mime_type' => $mime_type ) );
+	$editor = wp_get_image_editor( $file );
 
 	if ( is_wp_error( $editor ) ) {
 		// The image cannot be edited.
 		return $image_meta;
 	}
 
-	$editor->set_output_mime_type( $mime_type );
-
 	// If stored EXIF data exists, rotate the source image before creating sub-sizes.
 	if ( ! empty( $image_meta['image_meta'] ) ) {
 		$rotated = $editor->maybe_exif_rotate();
@@ -604,22 +457,7 @@ function _wp_make_subsizes( $new_sizes, $file, $image_meta, $attachment_id, $mim
 				// TODO: Log errors.
 			} else {
 				// Save the size meta value.
-				if ( ! isset( $image_meta['sizes'][ $new_size_name ] ) ) {
-					$image_meta['sizes'][ $new_size_name ] = $new_size_meta;
-				} else {
-					// Remove any newly generated images that are larger than the primary mime type.
-					$new_size     = isset( $new_size_meta['filesize'] ) ? $new_size_meta['filesize'] : 0;
-					$primary_size = isset( $image_meta['sizes'][ $new_size_name ]['filesize'] ) ? $image_meta['sizes'][ $new_size_name ]['filesize'] : 0;
-
-					if ( $new_size && $primary_size && $new_size >= $primary_size ) {
-						wp_delete_file( dirname( $file ) . '/' . $new_size_meta['file'] );
-						continue;
-					}
-				}
-				if ( ! isset( $image_meta['sizes'][ $new_size_name ]['sources'] ) ) {
-					$image_meta['sizes'][ $new_size_name ]['sources'] = array();
-				}
-				$image_meta['sizes'][ $new_size_name ]['sources'][ $mime_type ] = _wp_get_sources_from_meta( $new_size_meta );
+				$image_meta['sizes'][ $new_size_name ] = $new_size_meta;
 				wp_update_attachment_metadata( $attachment_id, $image_meta );
 			}
 		}
@@ -628,112 +466,7 @@ function _wp_make_subsizes( $new_sizes, $file, $image_meta, $attachment_id, $mim
 		$created_sizes = $editor->multi_resize( $new_sizes );
 
 		if ( ! empty( $created_sizes ) ) {
-			foreach ( $created_sizes as $created_size_name => $created_size_meta ) {
-
-				// Primary mime type is set in 'sizes' array.
-				if ( ! isset( $image_meta['sizes'][ $created_size_name ] ) ) {
-					$image_meta['sizes'][ $created_size_name ] = $created_size_meta;
-				} else {
-					// Remove any newly generated images that are larger than the primary mime type.
-					$new_size     = isset( $created_size_meta['filesize'] ) ? $created_size_meta['filesize'] : 0;
-					$primary_size = isset( $image_meta['sizes'][ $created_size_name ]['filesize'] ) ? $image_meta['sizes'][ $created_size_name ]['filesize'] : 0;
-
-					if ( $new_size && $primary_size && $new_size >= $primary_size ) {
-						wp_delete_file( dirname( $file ) . '/' . $created_size_meta['file'] );
-						continue;
-					}
-				}
-				if ( ! isset( $image_meta['sizes'][ $created_size_name ]['sources'] ) ) {
-					$image_meta['sizes'][ $created_size_name ]['sources'] = array();
-				}
-				$image_meta['sizes'][ $created_size_name ]['sources'][ $mime_type ] = _wp_get_sources_from_meta( $created_size_meta );
-			}
-			wp_update_attachment_metadata( $attachment_id, $image_meta );
-		}
-	}
-
-	return $image_meta;
-}
-
-/**
- * Filters the list of image size objects that support secondary mime type output.
- *
- * @since 6.1.0
- *
- * @param array $sizes         Associative array of image sizes.
- * @param int   $attachment_id Attachment ID.
- * @return array $sizes Filtered $sizes with only those that support secondary mime type output.
- */
-function _wp_filter_image_sizes_additional_mime_type_support( $sizes, $attachment_id ) {
-
-	// Include only the core sizes that do not rely on add_image_size(). Additional image sizes are opt-in.
-	$enabled_sizes = array(
-		'thumbnail'      => true,
-		'medium'         => true,
-		'medium_large'   => true,
-		'large'          => true,
-		'post-thumbnail' => true,
-	);
-
-	/**
-	 * Filter the sizes that support secondary mime type output. Developers can use this
-	 * to control the output of additional mime type sub-sized images.
-	 *
-	 * @since 6.1.0
-	 *
-	 * @param array $enabled_sizes Map of size names and whether they support secondary mime type output.
-	 * @param int   $attachment_id Attachment ID.
-	 */
-	$enabled_sizes = apply_filters( 'wp_image_sizes_with_additional_mime_type_support', $enabled_sizes, $attachment_id );
-
-	// Filter supported sizes to only include enabled sizes.
-	return array_intersect_key( $sizes, array_filter( $enabled_sizes ) );
-}
-
-/**
- * Low-level function to create full-size images in additional mime types.
- *
- * Updates the image meta after each mime type image is created.
- *
- * @since 6.1.0
- * @access private
- *
- * @param array  $new_mime_types Array defining what mime types to create.
- * @param string $file           Full path to the image file.
- * @param array  $image_meta     The attachment meta data array.
- * @param int    $attachment_id  Attachment ID to process.
- * @return array The attachment meta data with updated `sizes` array. Includes an array of errors encountered while resizing.
- */
-function _wp_make_additional_mime_types( $new_mime_types, $file, $image_meta, $attachment_id ) {
-	$imagesize          = array(
-		$image_meta['width'],
-		$image_meta['height'],
-	);
-	$exif_meta          = isset( $image_meta['image_meta'] ) ? $image_meta['image_meta'] : null;
-	$original_file_size = isset( $image_meta['filesize'] ) ? $image_meta['filesize'] : wp_filesize( $file );
-
-	foreach ( $new_mime_types as $mime_type ) {
-		list( $editor, $resized, $rotated ) = _wp_maybe_scale_and_rotate_image( $file, $attachment_id, $imagesize, $exif_meta, $mime_type );
-		if ( is_wp_error( $editor ) ) {
-			// The image cannot be edited.
-			continue;
-		}
-
-		$suffix    = _wp_get_image_suffix( $resized, $rotated );
-		$extension = wp_get_default_extension_for_mime_type( $mime_type );
-
-		$saved = $editor->save( $editor->generate_filename( $suffix, null, $extension ) );
-
-		if ( is_wp_error( $saved ) ) {
-			// TODO: Log errors.
-		} else {
-			// If the saved image is larger than the original, discard it.
-			$filesize = isset( $saved['filesize'] ) ? $saved['filesize'] : wp_filesize( $saved['path'] );
-			if ( $filesize && $original_file_size && $filesize > $original_file_size ) {
-				wp_delete_file( $saved['path'] );
-				continue;
-			}
-			$image_meta['sources'][ $mime_type ] = _wp_get_sources_from_meta( $saved );
+			$image_meta['sizes'] = array_merge( $image_meta['sizes'], $created_sizes );
 			wp_update_attachment_metadata( $attachment_id, $image_meta );
 		}
 	}
@@ -827,9 +560,9 @@ function wp_generate_attachment_metadata( $attachment_id, $file ) {
 				 * @param array $uploaded         {
 				 *     Information about the newly-uploaded file.
 				 *
-				 *     @type string $file Filename of the newly-uploaded file.
-				 *     @type string $url  URL of the uploaded file.
-				 *     @type string $type File type.
+				 *     @type string $file  Filename of the newly-uploaded file.
+				 *     @type string $url   URL of the uploaded file.
+				 *     @type string $type  File type.
 				 * }
 				 */
 				$image_attachment = apply_filters( 'attachment_thumbnail_args', $image_attachment, $metadata, $uploaded );
@@ -897,7 +630,7 @@ function wp_generate_attachment_metadata( $attachment_id, $file ) {
 					wp_update_attachment_metadata( $attachment_id, $metadata );
 
 					// Create sub-sizes saving the image meta after each.
-					$metadata = _wp_make_subsizes( $merged_sizes, $image_file, $metadata, $attachment_id, '' );
+					$metadata = _wp_make_subsizes( $merged_sizes, $image_file, $metadata, $attachment_id );
 				}
 			}
 		}
@@ -1424,97 +1157,3 @@ function _copy_image_file( $attachment_id ) {
 
 	return $dst_file;
 }
-
-/**
- * Returns an array with the list of valid mime types that a specific mime type should be converted into.
- * For example an `image/jpeg` should be converted into an `image/jpeg` and `image/webp`. The first type
- * is considered the primary output type for this image.
- *
- * Called for each uploaded image to determine the list of mime types that should be converted into. Then,
- * called again for each image size as they are generated to check if the image should be converted into the mime type
- * for that size.
- *
- * @since 6.1.0
- *
- * @param int    $attachment_id The attachment ID.
- * @return array An array of valid mime types, where the key is the source file mime type and the list of mime types to
- *               generate.
- */
-function wp_upload_image_mime_transforms( $attachment_id ) {
-	$default_image_mime_transforms = array(
-		'image/jpeg' => array( 'image/jpeg', 'image/webp' ),
-		'image/webp' => array( 'image/webp', 'image/jpeg' ),
-	);
-	$image_mime_transforms         = $default_image_mime_transforms;
-
-	/**
-	 * Filters the output mime types for a given input mime type and image size.
-	 *
-	 * @since 6.1.0
-	 *
-	 * @param array $image_mime_transforms A map with the valid mime transforms where the key is the source file mime type
-	 *                                      and the value is one or more mime file types to generate.
-	 * @param int   $attachment_id         The ID of the attachment where the hook was dispatched.
-	 */
-	$image_mime_transforms = apply_filters( 'wp_upload_image_mime_transforms', $image_mime_transforms, $attachment_id );
-
-	if ( ! is_array( $image_mime_transforms ) ) {
-		return $default_image_mime_transforms;
-	}
-
-	return array_map(
-		function( $transforms_list ) {
-			return (array) $transforms_list;
-		},
-		$image_mime_transforms
-	);
-}
-
-/**
- * Extracts the primary and additional mime output types for an image from the $image_mime_transforms.
- *
- * @since 6.1.0
- * @access private
- *
- * @param string $file          Full path to the image file.
- * @param int    $attachment_id Attachment ID to process.
- * @return array An array with two entries, the primary mime type and the list of additional mime types.
- */
-function _wp_get_primary_and_additional_mime_types( $file, $attachment_id ) {
-	$image_mime_transforms = wp_upload_image_mime_transforms( $attachment_id );
-	$original_mime_type    = wp_get_image_mime( $file );
-	$output_mime_types     = isset( $image_mime_transforms[ $original_mime_type ] ) ? $image_mime_transforms[ $original_mime_type ] : array( $original_mime_type );
-
-	// Exclude any output mime types that the system doesn't support.
-	$output_mime_types = array_values(
-		array_filter(
-			$output_mime_types,
-			function( $mime_type ) {
-				return wp_image_editor_supports(
-					array(
-						'mime_type' => $mime_type,
-					)
-				);
-			}
-		)
-	);
-
-	// Handle an empty value for $output_mime_types: only output the original type.
-	if ( empty( $output_mime_types ) ) {
-		return array( $original_mime_type, array() );
-	}
-
-	// Use original mime type as primary mime type, or alternatively the first one.
-	$primary_mime_type_key = array_search( $original_mime_type, $output_mime_types, true );
-	if ( false === $primary_mime_type_key ) {
-		$primary_mime_type_key = 0;
-	}
-	// Split output mime types into primary mime type and additional mime types.
-	$additional_mime_types     = $output_mime_types;
-	list( $primary_mime_type ) = array_splice( $additional_mime_types, $primary_mime_type_key, 1 );
-
-	return array(
-		$primary_mime_type,
-		$additional_mime_types,
-	);
-}
diff --git src/wp-includes/class-wp-image-editor.php src/wp-includes/class-wp-image-editor.php
index ccf43402a6..caa3092d36 100644
--- src/wp-includes/class-wp-image-editor.php
+++ src/wp-includes/class-wp-image-editor.php
@@ -334,11 +334,6 @@ abstract class WP_Image_Editor {
 	protected function get_output_format( $filename = null, $mime_type = null ) {
 		$new_ext = null;
 
-		// If no mime type is passed but output mime type is set, use that.
-		if ( ! $mime_type && ! empty( $this->output_mime_type ) ) {
-			$mime_type = $this->output_mime_type;
-		}
-
 		// By default, assume specified type takes priority.
 		if ( $mime_type ) {
 			$new_ext = $this->get_extension( $mime_type );
@@ -430,25 +425,18 @@ abstract class WP_Image_Editor {
 	}
 
 	/**
-	 * Builds an output filename based on current file, and adding proper suffix.
+	 * Builds an output filename based on current file, and adding proper suffix
 	 *
 	 * @since 3.5.0
-	 * @since 6.1.0 Skips adding a suffix when set to an empty string. When the
-	 *              file extension being generated doesn't match the image file extension,
-	 *              add the extension to the suffix
-	 *
-	 * @param string $suffix    Optional. Suffix to add to the filename. The default null
-	 *                          will result in a 'widthxheight' suffix. Passing
-	 *                          an empty string will result in no suffix.
-	 * @param string $dest_path Optional. The path to save the file to. The default null
-	 *                          will use the image file path.
-	 * @param string $extension Optional. The file extension to use. The default null
-	 *                          will use the image file extension.
-	 * @return string filename The generated file name.
+	 *
+	 * @param string $suffix
+	 * @param string $dest_path
+	 * @param string $extension
+	 * @return string filename
 	 */
 	public function generate_filename( $suffix = null, $dest_path = null, $extension = null ) {
 		// $suffix will be appended to the destination filename, just before the extension.
-		if ( null === $suffix ) {
+		if ( ! $suffix ) {
 			$suffix = $this->get_suffix();
 		}
 
@@ -469,21 +457,7 @@ abstract class WP_Image_Editor {
 			}
 		}
 
-		if ( empty( $suffix ) ) {
-			$suffix = '';
-		} else {
-			$suffix = "-{$suffix}";
-		}
-
-		// When the file extension being generated doesn't match the image file extension,
-		// add the extension to the suffix to ensure a unique file name. Prevents
-		// name conflicts when a single image type can have multiple extensions,
-		// eg. .jpg, .jpeg and .jpe are all valid JPEG extensions.
-		if ( ! empty( $extension ) && $extension !== $ext ) {
-			$suffix .= "-{$ext}";
-		}
-
-		return trailingslashit( $dir ) . "{$name}{$suffix}.{$new_ext}";
+		return trailingslashit( $dir ) . "{$name}-{$suffix}.{$new_ext}";
 	}
 
 	/**
@@ -663,28 +637,5 @@ abstract class WP_Image_Editor {
 
 		return wp_get_default_extension_for_mime_type( $mime_type );
 	}
-
-	/**
-	 * Set the editor output mime type, useful when outputting alternate mime types.
-	 *
-	 * Track that the mime type is set with the mime type set flag.
-	 *
-	 * @since 6.1.0
-	 *
-	 * @param string $output_mime_type The mime type to set.
-	 */
-	public function set_output_mime_type( $output_mime_type ) {
-		$this->output_mime_type = $output_mime_type;
-	}
-
-	/**
-	 * Reset the mime type to the original file mime type.
-	 *
-	 * Reset the mime type set flag.
-	 *
-	 * @since 6.1.0
-	 */
-	public function reset_output_mime_type() {
-		$this->output_mime_type = $this->mime_type;
-	}
 }
+
diff --git src/wp-includes/media.php src/wp-includes/media.php
index 456cd7c988..e398644178 100644
--- src/wp-includes/media.php
+++ src/wp-includes/media.php
@@ -1852,11 +1852,6 @@ function wp_filter_content_tags( $content, $context = null ) {
 				$filtered_image = wp_img_tag_add_decoding_attr( $filtered_image, $context );
 			}
 
-			// Use alternate mime types when specified and available.
-			if ( $attachment_id > 0 && _wp_in_front_end_context() ) {
-				$filtered_image = wp_image_use_alternate_mime_types( $filtered_image, $context, $attachment_id );
-			}
-
 			/**
 			 * Filters an img tag within the content for a given context.
 			 *
@@ -1903,117 +1898,6 @@ function wp_filter_content_tags( $content, $context = null ) {
 	return $content;
 }
 
-/**
- * Use alternate mime type images in the front end content output when available.
- *
- * @since 6.1.0
- *
- * @param string $image         The HTML `img` tag where the attribute should be added.
- * @param string $context       Additional context to pass to the filters.
- * @param int    $attachment_id The attachment ID.
- * @return string Converted `img` tag with `loading` attribute added.
- */
-function wp_image_use_alternate_mime_types( $image, $context, $attachment_id ) {
-	$metadata = wp_get_attachment_metadata( $attachment_id );
-	if ( empty( $metadata['file'] ) ) {
-		return $image;
-	}
-
-	// Only alter images with a `sources` attribute
-	if ( empty( $metadata['sources'] ) ) {
-		return $image;
-	};
-
-	$target_mimes = array( 'image/webp', 'image/jpeg' );
-
-	/**
-	 * Filter the content image mime type output selection and order.
-	 *
-	 * When outputting images in the content, the first mime type available will be used.
-	 *
-	 * @since 6.1.0
-	 *
-	 * @param array  $target_mimes  The image output mime type and order. Default is array( 'image/webp', 'image/jpeg' ).
-	 * @param int    $attachment_id The attachment ID.
-	 * @param string $context       Additional context to pass to the filters.
-	 * @return array The filtered output mime type and order. Return an empty array to skip mime type substitution.
-	 */
-	$target_mimes = apply_filters( 'wp_content_image_mimes', $target_mimes, $attachment_id, $context );
-
-	if ( false === $target_mimes ) {
-		return $image;
-	}
-
-	// Find the appropriate size for the provided URL in the first available mime type.
-	foreach ( $target_mimes as $target_mime ) {
-		// Handle full size image replacement.
-		if ( ! empty( $metadata['sources'][ $target_mime ]['file'] ) ) {
-			$src_filename = wp_basename( $metadata['file'] );
-
-			// This is the same MIME type as the original, so the entire $target_mime can be skipped.
-			// Since it is already the preferred MIME type, the entire loop can be cancelled.
-			if ( $metadata['sources'][ $target_mime ]['file'] === $src_filename ) {
-				break;
-			}
-
-			$image = str_replace( $src_filename, $metadata['sources'][ $target_mime ]['file'], $image );
-
-			// The full size was replaced, so unset this entirely here so that in the next iteration it is no longer
-			// considered, simply for a small performance optimization.
-			unset( $metadata['sources'] );
-		}
-
-		// Go through each image size and replace with the first available mime type version.
-		foreach ( $metadata['sizes'] as $name => $size_data ) {
-			// Check if size has an original file.
-			if ( empty( $size_data['file'] ) ) {
-				continue;
-			}
-
-			// Check if size has a source in the desired mime type.
-			if ( empty( $size_data['sources'][ $target_mime ]['file'] ) ) {
-				continue;
-			}
-
-			$src_filename = wp_basename( $size_data['file'] );
-
-			// This is the same MIME type as the original, so the entire $target_mime can be skipped.
-			// Since it is already the preferred MIME type, the entire loop can be cancelled.
-			if ( $size_data['sources'][ $target_mime ]['file'] === $src_filename ) {
-				break 2;
-			}
-
-			// Found a match, replace with the new filename.
-			$image = str_replace( $src_filename, $size_data['sources'][ $target_mime ]['file'], $image );
-
-			// This size was replaced, so unset this entirely here so that in the next iteration it is no longer
-			// considered, simply for a small performance optimization.
-			unset( $metadata['sizes'][ $name ] );
-		}
-	}
-	return $image;
-}
-
-/**
- * Check if execution is currently in the front end content context, outside of <head>.
- *
- * @since 6.1.0
- * @access private
- *
- * @return bool True if in the front end content context, false otherwise.
- */
-function _wp_in_front_end_context() {
-	global $wp_query;
-
-	// Check if this request is generally outside (or before) any frontend context.
-	if ( ! isset( $wp_query ) || defined( 'XMLRPC_REQUEST' ) || defined( 'REST_REQUEST' ) || is_feed() ) {
-		return false;
-	}
-
-	// Check if we're anywhere before the 'wp_head' action has completed.
-	return did_action( 'template_redirect' ) && ! doing_action( 'wp_head' );
-}
-
 /**
  * Adds `loading` attribute to an `img` HTML tag.
  *
diff --git src/wp-includes/post.php src/wp-includes/post.php
index 244047659d..6a0af16a8b 100644
--- src/wp-includes/post.php
+++ src/wp-includes/post.php
@@ -6486,28 +6486,13 @@ function wp_delete_attachment_files( $post_id, $meta, $backup_sizes, $file ) {
 		$intermediate_dir = path_join( $uploadpath['basedir'], dirname( $file ) );
 
 		foreach ( $meta['sizes'] as $size => $sizeinfo ) {
+			$intermediate_file = str_replace( wp_basename( $file ), $sizeinfo['file'], $file );
 
-			// Check for alternate size mime types in the sizeinfo['sources'] array to delete.
-			if ( isset( $sizeinfo['sources'] ) && is_array( $sizeinfo['sources'] ) ) {
-				foreach ( $sizeinfo['sources'] as $mime => $properties ) {
-					$intermediate_file = str_replace( wp_basename( $file ), $properties['file'], $file );
-					if ( ! empty( $intermediate_file ) ) {
-						$intermediate_file = path_join( $uploadpath['basedir'], $intermediate_file );
-						if ( ! wp_delete_file_from_directory( $intermediate_file, $intermediate_dir ) ) {
-							$deleted = false;
-						}
-					}
-				}
-			} else {
-				// Otherwise, delete files from the sizeinfo data.
-				$intermediate_file = str_replace( wp_basename( $file ), $sizeinfo['file'], $file );
+			if ( ! empty( $intermediate_file ) ) {
+				$intermediate_file = path_join( $uploadpath['basedir'], $intermediate_file );
 
-				if ( ! empty( $intermediate_file ) ) {
-					$intermediate_file = path_join( $uploadpath['basedir'], $intermediate_file );
-
-					if ( ! wp_delete_file_from_directory( $intermediate_file, $intermediate_dir ) ) {
-						$deleted = false;
-					}
+				if ( ! wp_delete_file_from_directory( $intermediate_file, $intermediate_dir ) ) {
+					$deleted = false;
 				}
 			}
 		}
@@ -6529,60 +6514,26 @@ function wp_delete_attachment_files( $post_id, $meta, $backup_sizes, $file ) {
 		}
 	}
 
-	// Delete the full size images from 'sources' if available, or the root file.
-	if ( isset( $meta['sources'] ) && is_array( $meta['sources'] ) ) {
-		$sources          = $meta['sources'];
-		$intermediate_dir = path_join( $uploadpath['basedir'], dirname( $file ) );
-		foreach ( $sources as $mime => $properties ) {
-			if ( ! is_array( $properties ) || empty( $properties['file'] ) ) {
-				continue;
-			}
-			$intermediate_file = str_replace( wp_basename( $file ), $properties['file'], $file );
-			if ( ! wp_delete_file_from_directory( $intermediate_file, $intermediate_dir ) ) {
-				$deleted = false;
-			}
-		}
-	} else {
-		if ( ! wp_delete_file_from_directory( $file, $uploadpath['basedir'] ) ) {
-			$deleted = false;
-		}
-	}
-
 	if ( is_array( $backup_sizes ) ) {
-
 		$del_dir = path_join( $uploadpath['basedir'], dirname( $meta['file'] ) );
-		// Delete the root (edited) file which was not deleted above.
-		if ( ! wp_delete_file_from_directory( $file, $uploadpath['basedir'] ) ) {
-			$deleted = false;
-		}
+
 		foreach ( $backup_sizes as $size ) {
-			// Delete files from 'sources' data if available, otherwise from 'sizes' data.
-			if ( isset( $meta['sources'] ) && is_array( $meta['sources'] ) ) {
-				// Delete any backup images stored in the 'sources' array.
-				if ( isset( $size['sources'] ) && is_array( $size['sources'] ) ) {
-					foreach ( $size['sources'] as $mime => $properties ) {
-						$del_file = path_join( dirname( $meta['file'] ), $properties['file'] );
-						if ( ! empty( $del_file ) ) {
-							$del_file = path_join( $uploadpath['basedir'], $del_file );
-							if ( ! wp_delete_file_from_directory( $del_file, $del_dir ) ) {
-								$deleted = false;
-							}
-						}
-					}
-				}
-			} else {
-				$del_file = path_join( dirname( $meta['file'] ), $size['file'] );
+			$del_file = path_join( dirname( $meta['file'] ), $size['file'] );
 
-				if ( ! empty( $del_file ) ) {
-					$del_file = path_join( $uploadpath['basedir'], $del_file );
-					if ( ! wp_delete_file_from_directory( $del_file, $del_dir ) ) {
-						$deleted = false;
-					}
+			if ( ! empty( $del_file ) ) {
+				$del_file = path_join( $uploadpath['basedir'], $del_file );
+
+				if ( ! wp_delete_file_from_directory( $del_file, $del_dir ) ) {
+					$deleted = false;
 				}
 			}
 		}
 	}
 
+	if ( ! wp_delete_file_from_directory( $file, $uploadpath['basedir'] ) ) {
+		$deleted = false;
+	}
+
 	return $deleted;
 }
 
diff --git src/wp-includes/rest-api/endpoints/class-wp-rest-attachments-controller.php src/wp-includes/rest-api/endpoints/class-wp-rest-attachments-controller.php
index fdb08e78bb..423347a721 100644
--- src/wp-includes/rest-api/endpoints/class-wp-rest-attachments-controller.php
+++ src/wp-includes/rest-api/endpoints/class-wp-rest-attachments-controller.php
@@ -783,15 +783,6 @@ class WP_REST_Attachments_Controller extends WP_REST_Posts_Controller {
 					}
 
 					$size_data['source_url'] = $image_src[0];
-
-					if ( empty( $size_data['sources'] ) || ! is_array( $size_data['sources'] ) ) {
-						continue;
-					}
-
-					$image_url_basename = wp_basename( $image_src[0] );
-					foreach ( $size_data['sources'] as $mime => &$mime_details ) {
-						$mime_details['source_url'] = str_replace( $image_url_basename, $mime_details['file'], $image_src[0] );
-					}
 				}
 
 				$full_src = wp_get_attachment_image_src( $post->ID, 'full' );
@@ -804,15 +795,6 @@ class WP_REST_Attachments_Controller extends WP_REST_Posts_Controller {
 						'mime_type'  => $post->post_mime_type,
 						'source_url' => $full_src[0],
 					);
-
-					if ( ! empty( $data['media_details']['sources'] ) ) {
-						$full_url_basename = wp_basename( $full_src[0] );
-						foreach ( $data['media_details']['sources'] as $mime => &$mime_details ) {
-							$mime_details['source_url'] = str_replace( $full_url_basename, $mime_details['file'], $full_src[0] );
-						}
-						$data['media_details']['sizes']['full']['sources'] = $data['media_details']['sources'];
-						unset( $data['media_details']['sources'] );
-					}
 				}
 			} else {
 				$data['media_details']['sizes'] = new stdClass;
diff --git tests/phpunit/tests/image/editor.php tests/phpunit/tests/image/editor.php
index c051ffec2b..487dad0664 100644
--- tests/phpunit/tests/image/editor.php
+++ tests/phpunit/tests/image/editor.php
@@ -131,7 +131,6 @@ class Tests_Image_Editor extends WP_Image_UnitTestCase {
 		$this->assertSame( 86, $editor->get_quality(), 'Output image format is WEBP. Quality setting for it should be 86.' );
 
 		// Removing PNG to WEBP conversion on save. Quality setting should reset to the default.
-		$editor->reset_output_mime_type();
 		remove_filter( 'image_editor_output_format', array( $this, 'image_editor_output_formats' ) );
 		$editor->save();
 		$this->assertSame( 82, $editor->get_quality(), 'After removing image conversion quality setting should reset to the default of 82.' );
@@ -155,7 +154,6 @@ class Tests_Image_Editor extends WP_Image_UnitTestCase {
 		$this->assertSame( 42, $editor->get_quality(), 'Image conversion from JPEG to WEBP. Filtered WEBP quality shoild be 42.' );
 
 		// After removing the conversion the quality setting should reset to the filtered value for the original image type, JPEG.
-		$editor->reset_output_mime_type();
 		remove_filter( 'image_editor_output_format', array( $this, 'image_editor_output_formats' ) );
 		$editor->save();
 		$this->assertSame(
@@ -228,10 +226,10 @@ class Tests_Image_Editor extends WP_Image_UnitTestCase {
 		$this->assertSame( trailingslashit( realpath( get_temp_dir() ) ), trailingslashit( realpath( dirname( $editor->generate_filename( null, get_temp_dir() ) ) ) ) );
 
 		// Test with a suffix only.
-		$this->assertSame( 'canola-100x50-jpg.png', wp_basename( $editor->generate_filename( null, null, 'png' ) ) );
+		$this->assertSame( 'canola-100x50.png', wp_basename( $editor->generate_filename( null, null, 'png' ) ) );
 
 		// Combo!
-		$this->assertSame( trailingslashit( realpath( get_temp_dir() ) ) . 'canola-new-jpg.png', $editor->generate_filename( 'new', realpath( get_temp_dir() ), 'png' ) );
+		$this->assertSame( trailingslashit( realpath( get_temp_dir() ) ) . 'canola-new.png', $editor->generate_filename( 'new', realpath( get_temp_dir() ), 'png' ) );
 
 		// Test with a stream destination.
 		$this->assertSame( 'file://testing/path/canola-100x50.jpg', $editor->generate_filename( null, 'file://testing/path' ) );
@@ -364,404 +362,4 @@ class Tests_Image_Editor extends WP_Image_UnitTestCase {
 		);
 	}
 
-	/**
-	 * Test creating  the original image mime type when the image is uploaded.
-	 *
-	 * @ticket 55443
-	 *
-	 * @dataProvider provider_image_with_default_behaviors_during_upload
-	 */
-	public function it_should_create_the_original_image_mime_type_when_the_image_is_uploaded( $file_location, $expected_mime, $targeted_mime ) {
-		$attachment_id = $this->factory->attachment->create_upload_object( $file_location );
-
-		$metadata = wp_get_attachment_metadata( $attachment_id );
-
-		$this->assertIsArray( $metadata );
-		foreach ( $metadata['sizes'] as $size_name => $properties ) {
-			$this->assertArrayHasKey( 'sources', $properties );
-			$this->assertIsArray( $properties['sources'] );
-			$this->assertArrayHasKey( $expected_mime, $properties['sources'] );
-			$this->assertArrayHasKey( 'filesize', $properties['sources'][ $expected_mime ] );
-			$this->assertArrayHasKey( 'file', $properties['sources'][ $expected_mime ] );
-			$this->assertArrayHasKey( $targeted_mime, $properties['sources'] );
-			$this->assertArrayHasKey( 'filesize', $properties['sources'][ $targeted_mime ] );
-			$this->assertArrayHasKey( 'file', $properties['sources'][ $targeted_mime ] );
-		}
-	}
-
-	/**
-	 * Data provider for it_should_create_the_original_image_mime_type_when_the_image_is_uploaded.
-	 */
-	public function provider_image_with_default_behaviors_during_upload() {
-		yield 'JPEG image' => array(
-			DIR_TESTDATA . '/images/test-image.jpg',
-			'image/jpeg',
-			'image/webp',
-		);
-
-		yield 'WebP image' => array(
-			DIR_TESTDATA . '/images/webp-lossy.webp',
-			'image/webp',
-			'image/jpeg',
-		);
-	}
-
-	/**
-	 * Test Do not create the sources property if no transform is provided.
-	 *
-	 * @ticket 55443
-	 */
-	public function it_should_not_create_the_sources_property_if_no_transform_is_provided() {
-		add_filter( 'wp_upload_image_mime_transforms', '__return_empty_array' );
-
-		$attachment_id = $this->factory->attachment->create_upload_object(
-			DIR_TESTDATA . '/images/test-image.jpg'
-		);
-
-		$metadata = wp_get_attachment_metadata( $attachment_id );
-
-		$this->assertIsArray( $metadata );
-		foreach ( $metadata['sizes'] as $size_name => $properties ) {
-			$this->assertArrayNotHasKey( 'sources', $properties );
-		}
-	}
-
-	/**
-	 * Test creating the sources property when no transform is available.
-	 *
-	 * @ticket 55443
-	 */
-	public function it_should_create_the_sources_property_when_no_transform_is_available() {
-		add_filter(
-			'wp_upload_image_mime_transforms',
-			function () {
-				return array( 'image/jpeg' => array() );
-			}
-		);
-
-		$attachment_id = $this->factory->attachment->create_upload_object(
-			DIR_TESTDATA . '/images/test-image.jpg'
-		);
-
-		$metadata = wp_get_attachment_metadata( $attachment_id );
-
-		$this->assertIsArray( $metadata );
-		foreach ( $metadata['sizes'] as $size_name => $properties ) {
-			$this->assertArrayHasKey( 'sources', $properties );
-			$this->assertIsArray( $properties['sources'] );
-			$this->assertArrayHasKey( 'image/jpeg', $properties['sources'] );
-			$this->assertArrayHasKey( 'filesize', $properties['sources']['image/jpeg'] );
-			$this->assertArrayHasKey( 'file', $properties['sources']['image/jpeg'] );
-			$this->assertArrayNotHasKey( 'image/webp', $properties['sources'] );
-		}
-	}
-
-	/**
-	 * Test not creating the sources property if the mime is not specified on the transforms images.
-	 *
-	 * @ticket 55443
-	 */
-	public function it_should_not_create_the_sources_property_if_the_mime_is_not_specified_on_the_transforms_images() {
-		add_filter(
-			'wp_upload_image_mime_transforms',
-			function () {
-				return array( 'image/jpeg' => array() );
-			}
-		);
-
-		$attachment_id = $this->factory->attachment->create_upload_object(
-			DIR_TESTDATA . '/images/webp-lossy.webp'
-		);
-
-		$metadata = wp_get_attachment_metadata( $attachment_id );
-
-		$this->assertIsArray( $metadata );
-		foreach ( $metadata['sizes'] as $size_name => $properties ) {
-			$this->assertArrayNotHasKey( 'sources', $properties );
-		}
-	}
-
-
-	/**
-	 * Test creating a WebP version with all the required properties.
-	 *
-	 * @ticket 55443
-	 */
-	public function it_should_create_a_webp_version_with_all_the_required_properties() {
-		$attachment_id = $this->factory->attachment->create_upload_object(
-			DIR_TESTDATA . '/images/test-image.jpg'
-		);
-
-		$metadata = wp_get_attachment_metadata( $attachment_id );
-		$this->assertArrayHasKey( 'sources', $metadata['sizes']['thumbnail'] );
-		$this->assertArrayHasKey( 'image/jpeg', $metadata['sizes']['thumbnail']['sources'] );
-		$this->assertArrayHasKey( 'filesize', $metadata['sizes']['thumbnail']['sources']['image/jpeg'] );
-		$this->assertArrayHasKey( 'file', $metadata['sizes']['thumbnail']['sources']['image/jpeg'] );
-		$this->assertArrayHasKey( 'image/webp', $metadata['sizes']['thumbnail']['sources'] );
-		$this->assertArrayHasKey( 'filesize', $metadata['sizes']['thumbnail']['sources']['image/webp'] );
-		$this->assertArrayHasKey( 'file', $metadata['sizes']['thumbnail']['sources']['image/webp'] );
-		$this->assertStringEndsNotWith( '.jpeg', $metadata['sizes']['thumbnail']['sources']['image/webp']['file'] );
-		$this->assertStringEndsWith( '.webp', $metadata['sizes']['thumbnail']['sources']['image/webp']['file'] );
-	}
-
-	/**
-	 * Test removing `scaled` suffix from the generated filename.
-	 *
-	 * @ticket 55443
-	 */
-	public function it_should_remove_scaled_suffix_from_the_generated_filename() {
-		// The leafs image is 1080 pixels wide with this filter we ensure a -scaled version is created.
-		add_filter(
-			'big_image_size_threshold',
-			function () {
-				return 850;
-			}
-		);
-
-		$attachment_id = $this->factory->attachment->create_upload_object(
-			DIR_TESTDATA . '/images/test-image.jpg'
-		);
-		$metadata      = wp_get_attachment_metadata( $attachment_id );
-		$this->assertStringEndsWith( '-scaled.jpg', get_attached_file( $attachment_id ) );
-		$this->assertArrayHasKey( 'image/webp', $metadata['sizes']['medium']['sources'] );
-		$this->assertStringEndsNotWith( '-scaled.webp', $metadata['sizes']['medium']['sources']['image/webp']['file'] );
-		$this->assertStringEndsWith( '-300x200.webp', $metadata['sizes']['medium']['sources']['image/webp']['file'] );
-	}
-
-	/**
-	 * Test removing the generated webp images when the attachment is deleted.
-	 *
-	 * @ticket 55443
-	 */
-	public function it_should_remove_the_generated_webp_images_when_the_attachment_is_deleted() {
-		// Make sure no editor is available.
-		$attachment_id = $this->factory->attachment->create_upload_object(
-			DIR_TESTDATA . '/images/test-image.jpg'
-		);
-
-		$file    = get_attached_file( $attachment_id, true );
-		$dirname = pathinfo( $file, PATHINFO_DIRNAME );
-
-		$this->assertIsString( $file );
-		$this->assertFileExists( $file );
-
-		$metadata = wp_get_attachment_metadata( $attachment_id );
-		$sizes    = array( 'thumbnail', 'medium' );
-
-		foreach ( $sizes as $size_name ) {
-			$this->assertArrayHasKey( 'image/webp', $metadata['sizes'][ $size_name ]['sources'] );
-			$this->assertArrayHasKey( 'file', $metadata['sizes'][ $size_name ]['sources']['image/webp'] );
-			$this->assertFileExists(
-				path_join( $dirname, $metadata['sizes'][ $size_name ]['sources']['image/webp']['file'] )
-			);
-		}
-
-		wp_delete_attachment( $attachment_id );
-
-		foreach ( $sizes as $size_name ) {
-			$this->assertFileDoesNotExist(
-				path_join( $dirname, $metadata['sizes'][ $size_name ]['sources']['image/webp']['file'] )
-			);
-		}
-	}
-
-	/**
-	 * Test removing the attached WebP version if the attachment is force deleted but empty trash day is not defined.
-	 *
-	 * @ticket 55443
-	 */
-	public function it_should_remove_the_attached_webp_version_if_the_attachment_is_force_deleted_but_empty_trash_day_is_not_defined() {
-		// Make sure no editor is available.
-		$attachment_id = $this->factory->attachment->create_upload_object(
-			DIR_TESTDATA . '/images/test-image.jpg'
-		);
-
-		$file    = get_attached_file( $attachment_id, true );
-		$dirname = pathinfo( $file, PATHINFO_DIRNAME );
-
-		$this->assertIsString( $file );
-		$this->assertFileExists( $file );
-
-		$metadata = wp_get_attachment_metadata( $attachment_id );
-
-		$this->assertFileExists(
-			path_join( $dirname, $metadata['sizes']['thumbnail']['sources']['image/webp']['file'] )
-		);
-
-		wp_delete_attachment( $attachment_id, true );
-
-		$this->assertFileDoesNotExist(
-			path_join( $dirname, $metadata['sizes']['thumbnail']['sources']['image/webp']['file'] )
-		);
-	}
-
-	/**
-	 * Test removing the WebP version of the image if the image is force deleted and empty trash days is set to zero.
-	 *
-	 * @ticket 55443
-	 */
-	public function it_should_remove_the_webp_version_of_the_image_if_the_image_is_force_deleted_and_empty_trash_days_is_set_to_zero() {
-		// Make sure no editor is available.
-		$attachment_id = $this->factory->attachment->create_upload_object(
-			DIR_TESTDATA . '/images/test-image.jpg'
-		);
-
-		$file    = get_attached_file( $attachment_id, true );
-		$dirname = pathinfo( $file, PATHINFO_DIRNAME );
-
-		$this->assertIsString( $file );
-		$this->assertFileExists( $file );
-
-		$metadata = wp_get_attachment_metadata( $attachment_id );
-
-		$this->assertFileExists(
-			path_join( $dirname, $metadata['sizes']['thumbnail']['sources']['image/webp']['file'] )
-		);
-
-		define( 'EMPTY_TRASH_DAYS', 0 );
-
-		wp_delete_attachment( $attachment_id, true );
-
-		$this->assertFileDoesNotExist(
-			path_join( $dirname, $metadata['sizes']['thumbnail']['sources']['image/webp']['file'] )
-		);
-	}
-
-	/**
-	 * Test avoiding the change of URLs of images that are not part of the media library.
-	 *
-	 * @ticket 55443
-	 */
-	public function it_should_avoid_the_change_of_urls_of_images_that_are_not_part_of_the_media_library() {
-		$paragraph = '<p>Donec accumsan, sapien et <img src="https://ia600200.us.archive.org/16/items/SPD-SLRSY-1867/hubblesite_2001_06.jpg">, id commodo nisi sapien et est. Mauris nisl odio, iaculis vitae pellentesque nec.</p>';
-
-		$this->assertSame( $paragraph, webp_uploads_update_image_references( $paragraph ) );
-	}
-
-	/**
-	 * Test avoiding replacing not existing attachment IDs.
-	 *
-	 * @ticket 55443
-	 */
-	public function it_should_avoid_replacing_not_existing_attachment_i_ds() {
-		$paragraph = '<p>Donec accumsan, sapien et <img class="wp-image-0" src="https://ia600200.us.archive.org/16/items/SPD-SLRSY-1867/hubblesite_2001_06.jpg">, id commodo nisi sapien et est. Mauris nisl odio, iaculis vitae pellentesque nec.</p>';
-
-		$this->assertSame( $paragraph, webp_uploads_update_image_references( $paragraph ) );
-	}
-
-	/**
-	 * Test preventing replacing a WebP image.
-	 *
-	 * @ticket 55443
-	 */
-	public function it_should_test_preventing_replacing_a_webp_image() {
-		$attachment_id = $this->factory->attachment->create_upload_object(
-			DIR_TESTDATA . '/images/webp-lossy.webp'
-		);
-
-		$tag = wp_get_attachment_image( $attachment_id, 'medium', false, array( 'class' => "wp-image-{$attachment_id}" ) );
-
-		$this->assertSame( $tag, webp_uploads_img_tag_update_mime_type( $tag, 'the_content', $attachment_id ) );
-	}
-
-	/**
-	 * Test preventing replacing a jpg image if the image does not have the target class name.
-	 *
-	 * @ticket 55443
-	 */
-	public function it_should_test_preventing_replacing_a_jpg_image_if_the_image_does_not_have_the_target_class_name() {
-		$attachment_id = $this->factory->attachment->create_upload_object(
-			DIR_TESTDATA . '/images/test-image.jpg'
-		);
-
-		$tag = wp_get_attachment_image( $attachment_id, 'medium' );
-
-		$this->assertSame( $tag, webp_uploads_update_image_references( $tag ) );
-	}
-
-	/**
-	 * Test replacing the references to a JPG image to a WebP version.
-	 *
-	 * @dataProvider provider_replace_images_with_different_extensions
-	 *
-	 * @ticket 55443
-	 */
-	public function it_should_replace_the_references_to_a_jpg_image_to_a_webp_version( $image_path ) {
-		$attachment_id = $this->factory->attachment->create_upload_object( $image_path );
-
-		$tag          = wp_get_attachment_image( $attachment_id, 'medium', false, array( 'class' => "wp-image-{$attachment_id}" ) );
-		$expected_tag = $tag;
-		$metadata     = wp_get_attachment_metadata( $attachment_id );
-		foreach ( $metadata['sizes'] as $size => $properties ) {
-			$expected_tag = str_replace( $properties['sources']['image/jpeg']['file'], $properties['sources']['image/webp']['file'], $expected_tag );
-		}
-
-		$this->assertNotEmpty( $expected_tag );
-		$this->assertNotSame( $tag, $expected_tag );
-		$this->assertSame( $expected_tag, webp_uploads_img_tag_update_mime_type( $tag, 'the_content', $attachment_id ) );
-	}
-
-	public function provider_replace_images_with_different_extensions() {
-		yield 'An image with a .jpg extension' => array( DIR_TESTDATA . '/images/test-image.jpg' );
-		yield 'An image with a .jpeg extension' => array( DIR_TESTDATA . '/images/test-image.jpeg' );
-	}
-
-	/**
-	 * Test the full image size from the original mime type.
-	 *
-	 * @ticket 55443
-	 */
-	public function it_should_contain_the_full_image_size_from_the_original_mime() {
-		$attachment_id = $this->factory->attachment->create_upload_object(
-			DIR_TESTDATA . '/images/test-image.jpg'
-		);
-
-		$tag = wp_get_attachment_image( $attachment_id, 'full', false, array( 'class' => "wp-image-{$attachment_id}" ) );
-
-		$expected = array(
-			'ext'  => 'jpg',
-			'type' => 'image/jpeg',
-		);
-		$this->assertSame( $expected, wp_check_filetype( get_attached_file( $attachment_id ) ) );
-		$this->assertContains( wp_basename( get_attached_file( $attachment_id ) ), webp_uploads_img_tag_update_mime_type( $tag, 'the_content', $attachment_id ) );
-	}
-
-	/**
-	 * Test preventing replacing an image with no available sources.
-	 *
-	 * @ticket 55443
-	 */
-	public function it_should_prevent_replacing_an_image_with_no_available_sources() {
-		add_filter( 'wp_upload_image_mime_transforms', '__return_empty_array' );
-
-		$attachment_id = $this->factory->attachment->create_upload_object( DIR_TESTDATA . '/images/test-image.jpg' );
-
-		$tag = wp_get_attachment_image( $attachment_id, 'full', false, array( 'class' => "wp-image-{$attachment_id}" ) );
-		$this->assertSame( $tag, webp_uploads_img_tag_update_mime_type( $tag, 'the_content', $attachment_id ) );
-	}
-
-	/**
-	 * Test preventing update not supported images with no available sources.
-	 *
-	 * @dataProvider provider_it_should_prevent_update_not_supported_images_with_no_available_sources
-	 *
-	 * @ticket 55443
-	 */
-	public function it_should_prevent_update_not_supported_images_with_no_available_sources( $image_path ) {
-		$attachment_id = $this->factory->attachment->create_upload_object( $image_path );
-
-		$this->assertIsNumeric( $attachment_id );
-		$tag = wp_get_attachment_image( $attachment_id, 'full', false, array( 'class' => "wp-image-{$attachment_id}" ) );
-
-		$this->assertSame( $tag, webp_uploads_img_tag_update_mime_type( $tag, 'the_content', $attachment_id ) );
-	}
-
-	/**
-	 * Data provider for it_should_prevent_update_not_supported_images_with_no_available_sources.
-	 */
-	public function provider_it_should_prevent_update_not_supported_images_with_no_available_sources() {
-		yield 'PNG image' => array( DIR_TESTDATA . '/images/test-image.png' );
-		yield 'GIFT image' => array( DIR_TESTDATA . '/images/test-image.gif' );
-	}
-
 }
diff --git tests/phpunit/tests/image/functions.php tests/phpunit/tests/image/functions.php
index cb5a7971c9..86d559145e 100644
--- tests/phpunit/tests/image/functions.php
+++ tests/phpunit/tests/image/functions.php
@@ -639,9 +639,6 @@ class Tests_Image_Functions extends WP_UnitTestCase {
 			$this->markTestSkipped( 'Rendering PDFs is not supported on this system.' );
 		}
 
-		// Use legacy JPEG output.
-		add_filter( 'wp_upload_image_mime_transforms', '__return_empty_array' );
-
 		$orig_file = DIR_TESTDATA . '/images/wordpress-gsoc-flyer.pdf';
 		$test_file = get_temp_dir() . 'wordpress-gsoc-flyer.pdf';
 		copy( $orig_file, $test_file );
@@ -680,12 +677,6 @@ class Tests_Image_Functions extends WP_UnitTestCase {
 					'height'    => 300,
 					'mime-type' => 'image/jpeg',
 					'filesize'  => wp_filesize( $temp_dir . 'wordpress-gsoc-flyer-pdf-232x300.jpg' ),
-					'sources'   => array(
-						'image/jpeg' => array(
-							'file'     => 'wordpress-gsoc-flyer-pdf-232x300.jpg',
-							'filesize' => wp_filesize( $temp_dir . 'wordpress-gsoc-flyer-pdf-232x300.jpg' ),
-						),
-					),
 				),
 				'large'     => array(
 					'file'      => 'wordpress-gsoc-flyer-pdf-791x1024.jpg',
@@ -693,12 +684,6 @@ class Tests_Image_Functions extends WP_UnitTestCase {
 					'height'    => 1024,
 					'mime-type' => 'image/jpeg',
 					'filesize'  => wp_filesize( $temp_dir . 'wordpress-gsoc-flyer-pdf-791x1024.jpg' ),
-					'sources'   => array(
-						'image/jpeg' => array(
-							'file'     => 'wordpress-gsoc-flyer-pdf-791x1024.jpg',
-							'filesize' => wp_filesize( $temp_dir . 'wordpress-gsoc-flyer-pdf-791x1024.jpg' ),
-						),
-					),
 				),
 				'thumbnail' => array(
 					'file'      => 'wordpress-gsoc-flyer-pdf-116x150.jpg',
@@ -706,12 +691,6 @@ class Tests_Image_Functions extends WP_UnitTestCase {
 					'height'    => 150,
 					'mime-type' => 'image/jpeg',
 					'filesize'  => wp_filesize( $temp_dir . 'wordpress-gsoc-flyer-pdf-116x150.jpg' ),
-					'sources'   => array(
-						'image/jpeg' => array(
-							'file'     => 'wordpress-gsoc-flyer-pdf-116x150.jpg',
-							'filesize' => wp_filesize( $temp_dir . 'wordpress-gsoc-flyer-pdf-116x150.jpg' ),
-						),
-					),
 				),
 			),
 			'filesize' => wp_filesize( $test_file ),
@@ -723,7 +702,6 @@ class Tests_Image_Functions extends WP_UnitTestCase {
 		foreach ( $metadata['sizes'] as $size ) {
 			unlink( $temp_dir . $size['file'] );
 		}
-		remove_filter( 'wp_upload_image_mime_transforms', '__return_empty_array' );
 	}
 
 	/**
@@ -738,9 +716,6 @@ class Tests_Image_Functions extends WP_UnitTestCase {
 
 		update_option( 'medium_crop', 1 );
 
-		// Use legacy JPEG output.
-		add_filter( 'wp_upload_image_mime_transforms', '__return_empty_array' );
-
 		$orig_file = DIR_TESTDATA . '/images/wordpress-gsoc-flyer.pdf';
 		$test_file = get_temp_dir() . 'wordpress-gsoc-flyer.pdf';
 		copy( $orig_file, $test_file );
@@ -779,12 +754,6 @@ class Tests_Image_Functions extends WP_UnitTestCase {
 					'height'    => 300,
 					'mime-type' => 'image/jpeg',
 					'filesize'  => wp_filesize( $temp_dir . 'wordpress-gsoc-flyer-pdf-300x300.jpg' ),
-					'sources'   => array(
-						'image/jpeg' => array(
-							'file'     => 'wordpress-gsoc-flyer-pdf-300x300.jpg',
-							'filesize' => wp_filesize( $temp_dir . 'wordpress-gsoc-flyer-pdf-300x300.jpg' ),
-						),
-					),
 				),
 				'large'     => array(
 					'file'      => 'wordpress-gsoc-flyer-pdf-791x1024.jpg',
@@ -792,13 +761,6 @@ class Tests_Image_Functions extends WP_UnitTestCase {
 					'height'    => 1024,
 					'mime-type' => 'image/jpeg',
 					'filesize'  => wp_filesize( $temp_dir . 'wordpress-gsoc-flyer-pdf-791x1024.jpg' ),
-					'sources'   => array(
-						'image/jpeg' => array(
-							'file'     => 'wordpress-gsoc-flyer-pdf-791x1024.jpg',
-							'filesize' => wp_filesize( $temp_dir . 'wordpress-gsoc-flyer-pdf-791x1024.jpg' ),
-						),
-					),
-
 				),
 				'thumbnail' => array(
 					'file'      => 'wordpress-gsoc-flyer-pdf-116x150.jpg',
@@ -806,12 +768,6 @@ class Tests_Image_Functions extends WP_UnitTestCase {
 					'height'    => 150,
 					'mime-type' => 'image/jpeg',
 					'filesize'  => wp_filesize( $temp_dir . 'wordpress-gsoc-flyer-pdf-116x150.jpg' ),
-					'sources'   => array(
-						'image/jpeg' => array(
-							'file'     => 'wordpress-gsoc-flyer-pdf-116x150.jpg',
-							'filesize' => wp_filesize( $temp_dir . 'wordpress-gsoc-flyer-pdf-116x150.jpg' ),
-						),
-					),
 				),
 			),
 			'filesize' => wp_filesize( $test_file ),
@@ -823,8 +779,6 @@ class Tests_Image_Functions extends WP_UnitTestCase {
 		foreach ( $metadata['sizes'] as $size ) {
 			unlink( $temp_dir . $size['file'] );
 		}
-		remove_filter( 'wp_upload_image_mime_transforms', '__return_empty_array' );
-
 	}
 
 	/**
@@ -835,9 +789,6 @@ class Tests_Image_Functions extends WP_UnitTestCase {
 			$this->markTestSkipped( 'Rendering PDFs is not supported on this system.' );
 		}
 
-		// Use legacy JPEG output.
-		add_filter( 'wp_upload_image_mime_transforms', '__return_empty_array' );
-
 		$orig_file = DIR_TESTDATA . '/images/wordpress-gsoc-flyer.pdf';
 		$test_file = get_temp_dir() . 'wordpress-gsoc-flyer.pdf';
 		copy( $orig_file, $test_file );
@@ -870,12 +821,6 @@ class Tests_Image_Functions extends WP_UnitTestCase {
 			'height'    => 100,
 			'mime-type' => 'image/jpeg',
 			'filesize'  => wp_filesize( $temp_dir . 'wordpress-gsoc-flyer-pdf-77x100.jpg' ),
-			'sources'   => array(
-				'image/jpeg' => array(
-					'file'     => 'wordpress-gsoc-flyer-pdf-77x100.jpg',
-					'filesize' => wp_filesize( $temp_dir . 'wordpress-gsoc-flyer-pdf-77x100.jpg' ),
-				),
-			),
 		);
 
 		// Different environments produce slightly different filesize results.
@@ -891,7 +836,6 @@ class Tests_Image_Functions extends WP_UnitTestCase {
 		foreach ( $metadata['sizes'] as $size ) {
 			unlink( $temp_dir . $size['file'] );
 		}
-		remove_filter( 'wp_upload_image_mime_transforms', '__return_empty_array' );
 	}
 
 	public function filter_fallback_intermediate_image_sizes( $fallback_sizes, $metadata ) {
@@ -1082,431 +1026,4 @@ class Tests_Image_Functions extends WP_UnitTestCase {
 			),
 		);
 	}
-
-	/**
-	 * @ticket 55443
-	 */
-	public function test_wp_upload_image_mime_transforms_generates_webp_and_jpeg_for_both_by_default() {
-		$result = wp_upload_image_mime_transforms( 42 );
-		$this->assertArrayHasKey( 'image/jpeg', $result );
-		$this->assertArrayHasKey( 'image/webp', $result );
-		$this->assertSameSets( array( 'image/jpeg', 'image/webp' ), $result['image/jpeg'] );
-		$this->assertSameSets( array( 'image/jpeg', 'image/webp' ), $result['image/webp'] );
-	}
-
-	/**
-	 * @ticket 55443
-	 */
-	public function test_wp_upload_image_mime_transforms_filter_always_use_webp_instead_of_jpeg() {
-		add_filter(
-			'wp_upload_image_mime_transforms',
-			function( $transforms ) {
-				// Ensure JPG only results in WebP files.
-				$transforms['image/jpeg'] = array( 'image/webp' );
-				// Unset WebP since it does not need any transformation in that case.
-				unset( $transforms['image/webp'] );
-				return $transforms;
-			}
-		);
-
-		$result = wp_upload_image_mime_transforms( 42 );
-		$this->assertArrayHasKey( 'image/jpeg', $result );
-		$this->assertArrayNotHasKey( 'image/webp', $result );
-		$this->assertSameSets( array( 'image/webp' ), $result['image/jpeg'] );
-	}
-
-	/**
-	 * @ticket 55443
-	 */
-	public function test_wp_upload_image_mime_transforms_filter_receives_parameters() {
-		$attachment_id = null;
-		add_filter(
-			'wp_upload_image_mime_transforms',
-			function( $transforms, $param1 ) use ( &$attachment_id ) {
-				$attachment_id = $param1;
-				return $transforms;
-			},
-			10,
-			2
-		);
-
-		wp_upload_image_mime_transforms( 23 );
-		$this->assertSame( 23, $attachment_id );
-	}
-
-	/**
-	 * @ticket 55443
-	 */
-	public function test_wp_upload_image_mime_transforms_filter_with_empty_array() {
-		add_filter( 'wp_upload_image_mime_transforms', '__return_empty_array' );
-		$result = wp_upload_image_mime_transforms( 42 );
-		$this->assertSame( array(), $result );
-	}
-
-	/**
-	 * @ticket 55443
-	 */
-	public function test_wp_upload_image_mime_transforms_filter_with_invalid_usage() {
-		$default = wp_upload_image_mime_transforms( 42 );
-
-		add_filter( 'wp_upload_image_mime_transforms', '__return_false' );
-		$result = wp_upload_image_mime_transforms( 42 );
-		$this->assertSame( $default, $result );
-	}
-
-	/**
-	 * @ticket 55443
-	 */
-	public function test__wp_get_primary_and_additional_mime_types_default() {
-		$jpeg_file = DIR_TESTDATA . '/images/test-image-large.jpg';
-
-		list( $primary_mime_type, $additional_mime_types ) = _wp_get_primary_and_additional_mime_types( $jpeg_file, 42 );
-		$this->assertSame( 'image/jpeg', $primary_mime_type );
-
-		// WebP may not be supported by the server, in which case it will be stripped from the results.
-		if ( wp_image_editor_supports( array( 'mime_type' => 'image/webp' ) ) ) {
-			$this->assertSame( array( 'image/webp' ), $additional_mime_types );
-		} else {
-			$this->assertSame( array(), $additional_mime_types );
-		}
-	}
-
-	/**
-	 * @ticket 55443
-	 */
-	public function test__wp_get_primary_and_additional_mime_types_prefer_original_mime() {
-		$jpeg_file = DIR_TESTDATA . '/images/test-image-large.jpg';
-
-		// Set 'image/jpeg' only as secondary output MIME type.
-		// Still, because it is the original, it should be chosen as primary over 'image/webp'.
-		add_filter(
-			'wp_upload_image_mime_transforms',
-			function( $transforms ) {
-				$transforms['image/jpeg'] = array( 'image/webp', 'image/jpeg' );
-				return $transforms;
-			}
-		);
-
-		list( $primary_mime_type, $additional_mime_types ) = _wp_get_primary_and_additional_mime_types( $jpeg_file, 42 );
-		$this->assertSame( 'image/jpeg', $primary_mime_type );
-
-		// WebP may not be supported by the server, in which case it will be stripped from the results.
-		if ( wp_image_editor_supports( array( 'mime_type' => 'image/webp' ) ) ) {
-			$this->assertSame( array( 'image/webp' ), $additional_mime_types );
-		} else {
-			$this->assertSame( array(), $additional_mime_types );
-		}
-	}
-
-	/**
-	 * @ticket 55443
-	 */
-	public function test__wp_get_primary_and_additional_mime_types_use_original_mime_when_no_transformation_rules() {
-		$jpeg_file = DIR_TESTDATA . '/images/test-image-large.jpg';
-
-		// Strip all transformation rules.
-		add_filter( 'wp_upload_image_mime_transforms', '__return_empty_array' );
-
-		list( $primary_mime_type, $additional_mime_types ) = _wp_get_primary_and_additional_mime_types( $jpeg_file, 42 );
-		$this->assertSame( 'image/jpeg', $primary_mime_type );
-		$this->assertSame( array(), $additional_mime_types );
-	}
-
-	/**
-	 * @ticket 55443
-	 */
-	public function test__wp_get_primary_and_additional_mime_types_different_output_mime() {
-		$jpeg_file = DIR_TESTDATA . '/images/test-image-large.jpg';
-
-		// Set 'image/webp' as the only output MIME type.
-		// In that case, JPEG is not generated at all, so WebP becomes the primary MIME type.
-		add_filter(
-			'wp_upload_image_mime_transforms',
-			function( $transforms ) {
-				$transforms['image/jpeg'] = array( 'image/webp' );
-				return $transforms;
-			}
-		);
-
-		list( $primary_mime_type, $additional_mime_types ) = _wp_get_primary_and_additional_mime_types( $jpeg_file, 42 );
-
-		// WebP may not be supported by the server, in which case it will fall back to the original MIME type.
-		if ( wp_image_editor_supports( array( 'mime_type' => 'image/webp' ) ) ) {
-			$this->assertSame( 'image/webp', $primary_mime_type );
-		} else {
-			$this->assertSame( 'image/jpeg', $primary_mime_type );
-		}
-
-		$this->assertSame( array(), $additional_mime_types );
-	}
-
-	/**
-	 * @ticket 55443
-	 */
-	public function test__wp_get_primary_and_additional_mime_types_different_output_mimes() {
-		$jpeg_file = DIR_TESTDATA . '/images/test-image-large.jpg';
-
-		// Set 'image/webp' and 'image/avif' as output MIME types.
-		// In that case, JPEG is not generated at all, with WebP being the primary MIME type and AVIF the secondary.
-		add_filter(
-			'wp_upload_image_mime_transforms',
-			function( $transforms ) {
-				$transforms['image/jpeg'] = array( 'image/webp', 'image/avif' );
-				return $transforms;
-			}
-		);
-
-		list( $primary_mime_type, $additional_mime_types ) = _wp_get_primary_and_additional_mime_types( $jpeg_file, 42 );
-
-		// WebP may not be supported by the server, in which case it will fall back to the original MIME type.
-		if ( wp_image_editor_supports( array( 'mime_type' => 'image/webp' ) ) ) {
-			$this->assertSame( 'image/webp', $primary_mime_type );
-		} else {
-			$this->assertSame( 'image/jpeg', $primary_mime_type );
-		}
-
-		// AVIF may not be supported by the server, in which case it will be stripped from the results.
-		if ( wp_image_editor_supports( array( 'mime_type' => 'image/avif' ) ) ) {
-			$this->assertSame( array( 'image/avif' ), $additional_mime_types );
-		} else {
-			$this->assertSame( array(), $additional_mime_types );
-		}
-	}
-
-	/**
-	 * @ticket 55443
-	 * @dataProvider data__wp_filter_image_sizes_additional_mime_type_support
-	 */
-	public function test__wp_filter_image_sizes_additional_mime_type_support( $input_size_data, $filter_callback, $expected_size_names ) {
-		remove_all_filters( 'wp_image_sizes_with_additional_mime_type_support' );
-		if ( $filter_callback ) {
-			add_filter( 'wp_image_sizes_with_additional_mime_type_support', $filter_callback );
-		}
-
-		$expected_size_data = array_intersect_key( $input_size_data, array_flip( $expected_size_names ) );
-
-		$output_size_data = _wp_filter_image_sizes_additional_mime_type_support( $input_size_data, 42 );
-		$this->assertEqualSetsWithIndex( $expected_size_data, $output_size_data );
-	}
-
-	public function data__wp_filter_image_sizes_additional_mime_type_support() {
-		$thumbnail_data    = array(
-			'width'  => 150,
-			'height' => 150,
-			'crop'   => true,
-		);
-		$medium_data       = array(
-			'width'  => 300,
-			'height' => 300,
-			'crop'   => false,
-		);
-		$medium_large_data = array(
-			'width'  => 768,
-			'height' => 0,
-			'crop'   => false,
-		);
-		$large_data        = array(
-			'width'  => 1024,
-			'height' => 1024,
-			'crop'   => false,
-		);
-		$custom_data       = array(
-			'width'  => 512,
-			'height' => 512,
-			'crop'   => true,
-		);
-
-		return array(
-			array(
-				array(
-					'thumbnail'    => $thumbnail_data,
-					'medium'       => $medium_data,
-					'medium_large' => $medium_large_data,
-					'large'        => $large_data,
-				),
-				null,
-				array( 'thumbnail', 'medium', 'medium_large', 'large' ),
-			),
-			array(
-				array(
-					'thumbnail' => $thumbnail_data,
-					'medium'    => $medium_data,
-					'custom'    => $custom_data,
-				),
-				null,
-				array( 'thumbnail', 'medium' ),
-			),
-			array(
-				array(
-					'thumbnail'    => $thumbnail_data,
-					'medium'       => $medium_data,
-					'medium_large' => $medium_large_data,
-					'large'        => $large_data,
-				),
-				function( $enabled_sizes ) {
-					unset( $enabled_sizes['medium_large'], $enabled_sizes['large'] );
-					return $enabled_sizes;
-				},
-				array( 'thumbnail', 'medium' ),
-			),
-			array(
-				array(
-					'thumbnail'    => $thumbnail_data,
-					'medium'       => $medium_data,
-					'medium_large' => $medium_large_data,
-					'large'        => $large_data,
-				),
-				function( $enabled_sizes ) {
-					$enabled_sizes['medium_large'] = false;
-					$enabled_sizes['large']        = false;
-					return $enabled_sizes;
-				},
-				array( 'thumbnail', 'medium' ),
-			),
-			array(
-				array(
-					'thumbnail' => $thumbnail_data,
-					'medium'    => $medium_data,
-					'custom'    => $custom_data,
-				),
-				function( $enabled_sizes ) {
-					unset( $enabled_sizes['medium'] );
-					$enabled_sizes['custom'] = true;
-					return $enabled_sizes;
-				},
-				array( 'thumbnail', 'custom' ),
-			),
-		);
-	}
-
-	/**
-	 * Test the `_wp_maybe_scale_and_rotate_image()` function.
-	 *
-	 * @dataProvider data_test__wp_maybe_scale_and_rotate_image
-	 *
-	 * @ticket 55443
-	 */
-	public function test__wp_maybe_scale_and_rotate_image( $file, $imagesize, $mime_type, $expected ) {
-		if ( ! wp_image_editor_supports( array( 'mime_type' => $mime_type ) ) ) {
-			$this->markTestSkipped( sprintf( 'This test requires %s support.', $mime_type ) );
-		}
-
-		$attributes    = array( 'post_mime_type' => $mime_type );
-		$attachment_id = $this->factory->attachment->create_object( $file, 0, $attributes );
-		$exif_meta     = wp_read_image_metadata( $file );
-
-		list( $editor, $resized, $rotated ) = _wp_maybe_scale_and_rotate_image( $file, $attachment_id, $imagesize, $exif_meta, $mime_type );
-
-		$this->assertSame( $expected['rotated'], $rotated );
-		$this->assertSame( $expected['resized'], $resized );
-		$this->assertSame( $expected['size'], $editor->get_size() );
-	}
-
-	/**
-	 * Data provider for the `test__wp_maybe_scale_and_rotate_image()` test.
-	 *
-	 * @return array
-	 */
-	public function data_test__wp_maybe_scale_and_rotate_image() {
-		return array(
-
-			// Image that will be scaled.
-			array(
-				DIR_TESTDATA . '/images/test-image-large.jpg',
-				array( 3000, 2250 ),
-				'image/jpeg',
-				array(
-					'rotated' => false,
-					'resized' => true,
-					'size'    => array(
-						'width'  => 2560,
-						'height' => 1920,
-					),
-				),
-			),
-
-			// Image that will not be scaled.
-			array(
-				DIR_TESTDATA . '/images/canola.jpg',
-				array( 640, 480 ),
-				'image/jpeg',
-				array(
-					'rotated' => false,
-					'resized' => false,
-					'size'    => array(
-						'width'  => 640,
-						'height' => 480,
-					),
-				),
-			),
-
-			// Image that will be flipped.
-			array(
-				DIR_TESTDATA . '/images/test-image-upside-down.jpg',
-				array( 600, 450 ),
-				'image/jpeg',
-				array(
-					'rotated' => true,
-					'resized' => false,
-					'size'    => array(
-						'width'  => 600,
-						'height' => 450,
-					),
-				),
-			),
-
-			// Image that will be rotated.
-			array(
-				DIR_TESTDATA . '/images/test-image-rotated-90ccw.jpg',
-				array( 1200, 1800 ),
-				'image/jpeg',
-				array(
-					'rotated' => true,
-					'resized' => false,
-					'size'    => array(
-						'width'  => 1800,
-						'height' => 1200,
-					),
-				),
-			),
-
-			// Image that will not be rotated - WebP Exif is not supported in PHP.
-			array(
-				DIR_TESTDATA . '/images/test-image-rotated-90cw.webp',
-				array( 1024, 768 ),
-				'image/webp',
-				array(
-					'rotated' => false,
-					'resized' => false,
-					'size'    => array(
-						'width'  => 1024,
-						'height' => 768,
-					),
-				),
-			),
-
-		);
-	}
-
-	/**
-	 * Test the `_wp_get_image_suffix()` function.
-	 * @dataProvider data_test__wp_get_image_suffix
-	 *
-	 * @ticket 55443
-	 */
-	public function test__wp_get_image_suffix( $resized, $rotated, $expected ) {
-		$this->assertSame( $expected, _wp_get_image_suffix( $resized, $rotated ) );
-	}
-
-	/**
-	 * Data provider for the `test__wp_get_image_suffix()` test.
-	 */
-	public function data_test__wp_get_image_suffix() {
-		return array(
-			array( false, false, '' ),
-			array( true, false, 'scaled' ),
-			array( false, true, 'rotated' ),
-			array( true, true, 'scaled' ),
-		);
-	}
 }
diff --git tests/phpunit/tests/media.php tests/phpunit/tests/media.php
index 7a1723af12..ba4bedf51e 100644
--- tests/phpunit/tests/media.php
+++ tests/phpunit/tests/media.php
@@ -2255,14 +2255,11 @@ EOF;
 		// Do not add width, height, and loading.
 		add_filter( 'wp_img_tag_add_width_and_height_attr', '__return_false' );
 		add_filter( 'wp_img_tag_add_loading_attr', '__return_false' );
-		add_filter( 'wp_content_image_mimes', '__return_empty_array' );
 
 		$this->assertSame( $content_filtered, wp_filter_content_tags( $content_unfiltered ) );
 
 		remove_filter( 'wp_img_tag_add_width_and_height_attr', '__return_false' );
 		remove_filter( 'wp_img_tag_add_loading_attr', '__return_false' );
-		remove_filter( 'wp_content_image_mimes', '__return_empty_array' );
-
 	}
 
 	/**
@@ -2296,12 +2293,9 @@ EOF;
 		$img = wp_img_tag_add_loading_attr( $img, 'test' );
 		$img = wp_img_tag_add_decoding_attr( $img, 'the_content' );
 		$img = preg_replace( '|<img ([^>]+) />|', '<img $1 ' . 'srcset="image2x.jpg 2x" />', $img );
-		add_filter( 'wp_content_image_mimes', '__return_empty_array' );
 
 		// The content filter should return the image unchanged.
 		$this->assertSame( $img, wp_filter_content_tags( $img ) );
-
-		remove_filter( 'wp_content_image_mimes', '__return_empty_array' );
 	}
 
 	/**
@@ -2371,7 +2365,6 @@ EOF;
 		add_filter( 'wp_img_tag_add_width_and_height_attr', '__return_false' );
 		add_filter( 'wp_img_tag_add_srcset_and_sizes_attr', '__return_false' );
 		add_filter( 'wp_img_tag_add_decoding_attr', '__return_false' );
-		add_filter( 'wp_content_image_mimes', '__return_empty_array' );
 
 		add_filter(
 			'wp_content_img_tag',
@@ -2434,7 +2427,6 @@ EOF;
 	 * @requires function imagejpeg
 	 */
 	public function test_wp_filter_content_tags_schemes() {
-		add_filter( 'wp_content_image_mimes', '__return_empty_array' );
 		$image_meta = wp_get_attachment_metadata( self::$large_id );
 		$size_array = $this->get_image_size_array_from_meta( $image_meta, 'medium' );
 
@@ -2480,7 +2472,6 @@ EOF;
 		$actual = wp_filter_content_tags( $unfiltered );
 
 		$this->assertSame( $expected, $actual );
-		remove_filter( 'wp_content_image_mimes', '__return_empty_array' );
 	}
 
 	/**
@@ -2974,13 +2965,11 @@ EOF;
 		// Do not add loading, srcset, and sizes.
 		add_filter( 'wp_img_tag_add_loading_attr', '__return_false' );
 		add_filter( 'wp_img_tag_add_srcset_and_sizes_attr', '__return_false' );
-		add_filter( 'wp_content_image_mimes', '__return_empty_array' );
 
 		$this->assertSame( $content_filtered, wp_filter_content_tags( $content_unfiltered ) );
 
 		remove_filter( 'wp_img_tag_add_loading_attr', '__return_false' );
 		remove_filter( 'wp_img_tag_add_srcset_and_sizes_attr', '__return_false' );
-		remove_filter( 'wp_content_image_mimes', '__return_empty_array' );
 	}
 
 	/**
@@ -3056,13 +3045,11 @@ EOF;
 		// Do not add width, height, srcset, and sizes.
 		add_filter( 'wp_img_tag_add_width_and_height_attr', '__return_false' );
 		add_filter( 'wp_img_tag_add_srcset_and_sizes_attr', '__return_false' );
-		add_filter( 'wp_content_image_mimes', '__return_empty_array' );
 
 		$this->assertSame( $content_filtered, wp_filter_content_tags( $content_unfiltered ) );
 
 		remove_filter( 'wp_img_tag_add_width_and_height_attr', '__return_false' );
 		remove_filter( 'wp_img_tag_add_srcset_and_sizes_attr', '__return_false' );
-		remove_filter( 'wp_content_image_mimes', '__return_empty_array' );
 	}
 
 	/**
@@ -3091,13 +3078,9 @@ EOF;
 		// Enable globally for all tags.
 		add_filter( 'wp_lazy_loading_enabled', '__return_true' );
 
-		add_filter( 'wp_content_image_mimes', '__return_empty_array' );
-
 		$this->assertSame( $content_filtered, wp_filter_content_tags( $content_unfiltered ) );
 		remove_filter( 'wp_lazy_loading_enabled', '__return_true' );
 		remove_filter( 'wp_img_tag_add_srcset_and_sizes_attr', '__return_false' );
-		remove_filter( 'wp_content_image_mimes', '__return_empty_array' );
-
 	}
 
 	/**
@@ -3122,12 +3105,9 @@ EOF;
 		// Disable globally for all tags.
 		add_filter( 'wp_lazy_loading_enabled', '__return_false' );
 
-		add_filter( 'wp_content_image_mimes', '__return_empty_array' );
-
 		$this->assertSame( $content, wp_filter_content_tags( $content ) );
 		remove_filter( 'wp_lazy_loading_enabled', '__return_false' );
 		remove_filter( 'wp_img_tag_add_srcset_and_sizes_attr', '__return_false' );
-		remove_filter( 'wp_content_image_mimes', '__return_empty_array' );
 	}
 
 	/**
@@ -3553,7 +3533,6 @@ EOF;
 	 */
 	function test_wp_filter_content_tags_with_wp_get_loading_attr_default() {
 		global $wp_query, $wp_the_query;
-		add_filter( 'wp_content_image_mimes', '__return_empty_array' );
 
 		$img1         = get_image_tag( self::$large_id, '', '', '', 'large' );
 		$iframe1      = '<iframe src="https://www.example.com" width="640" height="360"></iframe>';
@@ -3589,7 +3568,6 @@ EOF;
 			$content_filtered = wp_filter_content_tags( $content_unfiltered, 'the_content' );
 			remove_filter( 'wp_img_tag_add_srcset_and_sizes_attr', '__return_false' );
 		}
-		remove_filter( 'wp_content_image_mimes', '__return_empty_array' );
 
 		// After filtering, the first image should not be lazy-loaded while the other ones should be.
 		$this->assertSame( $content_expected, $content_filtered );
@@ -3639,169 +3617,6 @@ EOF;
 		// Clean up the above filter.
 		remove_filter( 'wp_omit_loading_attr_threshold', '__return_null', 100 );
 	}
-
-	/**
-	 * @ticket 55443
-	 */
-	public function test_wp_image_use_alternate_mime_types_replaces_jpg_with_webp_where_available() {
-		if ( ! wp_image_editor_supports( array( 'mime_type' => 'image/webp' ) ) ) {
-			$this->markTestSkipped( 'This test requires WebP support.' );
-		}
-
-		// The attachment $large_id is a JPEG image, so it gets WebP files generated by default.
-		$tag          = wp_get_attachment_image( self::$large_id, 'full' );
-		$expected_tag = $tag;
-
-		$metadata = wp_get_attachment_metadata( self::$large_id );
-		foreach ( $metadata['sizes'] as $size => $properties ) {
-			// Some sizes may not have WebP if the WebP file is larger than the JPEG for the size.
-			if ( ! isset( $properties['sources']['image/webp'] ) ) {
-				continue;
-			}
-			$expected_tag = str_replace( $properties['sources']['image/jpeg']['file'], $properties['sources']['image/webp']['file'], $expected_tag );
-		}
-		// Same applies to the full size.
-		if ( isset( $metadata['sources']['image/webp'] ) ) {
-			$expected_tag = str_replace( $metadata['sources']['image/jpeg']['file'], $metadata['sources']['image/webp']['file'], $expected_tag );
-		}
-
-		$this->assertNotSame( $tag, $expected_tag );
-		$this->assertSame( $expected_tag, wp_image_use_alternate_mime_types( $tag, 'the_content', self::$large_id ) );
-	}
-
-	/**
-	 * @ticket 55443
-	 */
-	public function test_wp_image_use_alternate_mime_types_does_not_replace_jpg_when_webp_is_not_available() {
-		if ( ! wp_image_editor_supports( array( 'mime_type' => 'image/webp' ) ) ) {
-			$this->markTestSkipped( 'This test requires WebP support.' );
-		}
-
-		// The attachment $large_id is a JPEG image, so it gets WebP files generated by default.
-		$tag = wp_get_attachment_image( self::$large_id, 'full' );
-
-		// Update attachment metadata as if the image had no WebP available for any sub-sizes and the full size.
-		$metadata = wp_get_attachment_metadata( self::$large_id );
-		foreach ( $metadata['sizes'] as $size => $properties ) {
-			unset( $metadata['sizes'][ $size ]['sources']['image/webp'] );
-		}
-		unset( $metadata['sources']['image/webp'] );
-		wp_update_attachment_metadata( self::$large_id, $metadata );
-
-		$this->assertSame( $tag, wp_image_use_alternate_mime_types( $tag, 'the_content', self::$large_id ) );
-	}
-
-	/**
-	 * @ticket 55443
-	 */
-	public function test_wp_image_use_alternate_mime_types_still_replaces_jpg_subsizes_when_webp_is_not_available_for_full_size() {
-		if ( ! wp_image_editor_supports( array( 'mime_type' => 'image/webp' ) ) ) {
-			$this->markTestSkipped( 'This test requires WebP support.' );
-		}
-
-		// The attachment $large_id is a JPEG image, so it gets WebP files generated by default.
-		$tag          = wp_get_attachment_image( self::$large_id, 'full' );
-		$expected_tag = $tag;
-
-		// Update attachment metadata as if the image had no WebP available for the full size.
-		$metadata = wp_get_attachment_metadata( self::$large_id );
-		unset( $metadata['sources']['image/webp'] );
-		wp_update_attachment_metadata( self::$large_id, $metadata );
-
-		foreach ( $metadata['sizes'] as $size => $properties ) {
-			// Some sizes may not have WebP if the WebP file is larger than the JPEG for the size.
-			if ( ! isset( $properties['sources']['image/webp'] ) ) {
-				continue;
-			}
-			$expected_tag = str_replace( $properties['sources']['image/jpeg']['file'], $properties['sources']['image/webp']['file'], $expected_tag );
-		}
-
-		$this->assertNotSame( $tag, $expected_tag );
-		$this->assertSame( $expected_tag, wp_image_use_alternate_mime_types( $tag, 'the_content', self::$large_id ) );
-	}
-
-	/**
-	 * @ticket 55443
-	 */
-	public function test_wp_image_use_alternate_mime_types_respects_wp_content_image_mimes_filter() {
-		if ( ! wp_image_editor_supports( array( 'mime_type' => 'image/webp' ) ) ) {
-			$this->markTestSkipped( 'This test requires WebP support.' );
-		}
-
-		// The attachment $large_id is a JPEG image, so it gets WebP files generated by default.
-		$tag = wp_get_attachment_image( self::$large_id, 'full' );
-
-		// Invalid filter value results in no changes to content.
-		add_filter( 'wp_content_image_mimes', '__return_false' );
-		$this->assertSame( $tag, wp_image_use_alternate_mime_types( $tag, 'the_content', self::$large_id ) );
-
-		// Empty array results in no changes to content.
-		add_filter( 'wp_content_image_mimes', '__return_empty_array' );
-		$this->assertSame( $tag, wp_image_use_alternate_mime_types( $tag, 'the_content', self::$large_id ) );
-
-		// Preferring JPEG over WebP results in no changes to content.
-		add_filter(
-			'wp_content_image_mimes',
-			function() {
-				return array( 'image/jpeg', 'image/webp' );
-			}
-		);
-		$this->assertSame( $tag, wp_image_use_alternate_mime_types( $tag, 'the_content', self::$large_id ) );
-	}
-
-	/**
-	 * @ticket 55443
-	 */
-	public function test__wp_in_front_end_context_without_wp_query() {
-		unset( $GLOBALS['wp_query'] );
-
-		$this->assertFalse( _wp_in_front_end_context() );
-	}
-
-	/**
-	 * @ticket 55443
-	 */
-	public function test__wp_in_front_end_context_with_feed() {
-		remove_all_actions( 'template_redirect' );
-		do_action( 'template_redirect' );
-		$GLOBALS['wp_query']->is_feed = true;
-
-		$this->assertFalse( _wp_in_front_end_context() );
-	}
-
-	/**
-	 * @ticket 55443
-	 */
-	public function test__wp_in_front_end_context_before_and_after_template_redirect() {
-		$result = _wp_in_front_end_context();
-
-		remove_all_actions( 'template_redirect' );
-		do_action( 'template_redirect' );
-
-		$this->assertFalse( $result );
-		$this->assertTrue( _wp_in_front_end_context() );
-	}
-
-	/**
-	 * @ticket 55443
-	 */
-	public function test__wp_in_front_end_context_within_wp_head() {
-		remove_all_actions( 'template_redirect' );
-		do_action( 'template_redirect' );
-
-		// Call function within a 'wp_head' callback.
-		remove_all_actions( 'wp_head' );
-		$result = null;
-		add_action(
-			'wp_head',
-			function() use ( &$result ) {
-				$result = _wp_in_front_end_context();
-			}
-		);
-		do_action( 'wp_head' );
-
-		$this->assertFalse( $result );
-	}
 }
 
 /**
diff --git tests/phpunit/tests/rest-api/rest-attachments-controller.php tests/phpunit/tests/rest-api/rest-attachments-controller.php
index 585b2b5b4f..106906ee2b 100644
--- tests/phpunit/tests/rest-api/rest-attachments-controller.php
+++ tests/phpunit/tests/rest-api/rest-attachments-controller.php
@@ -2262,46 +2262,4 @@ class WP_Test_REST_Attachments_Controller extends WP_Test_REST_Post_Type_Control
 			}
 		);
 	}
-
-	/**
-	 * @ticket 55443
-	 */
-	public function test_image_sources_to_rest_response() {
-
-		$attachment_id = self::factory()->attachment->create_upload_object( $this->test_file );
-		$metadata      = wp_get_attachment_metadata( $attachment_id );
-		$request       = new WP_REST_Request();
-		$request['id'] = $attachment_id;
-		$controller    = new WP_REST_Attachments_Controller( 'attachment' );
-		$response      = $controller->get_item( $request );
-
-		$this->assertNotWPError( $response );
-
-		$data       = $response->get_data();
-		$mime_types = array(
-			'image/jpeg',
-		);
-
-		if ( wp_image_editor_supports( array( 'mime_type' => 'image/webp' ) ) ) {
-			array_push( $mime_types, 'image/webp' );
-		}
-
-		foreach ( $data['media_details']['sizes'] as $size_name => $properties ) {
-			if ( ! isset( $metadata['sizes'][ $size_name ]['sources'] ) ) {
-				continue;
-			}
-
-			$this->assertArrayHasKey( 'sources', $properties );
-			$this->assertIsArray( $properties['sources'] );
-
-			foreach ( $mime_types as $mime_type ) {
-				$this->assertArrayHasKey( $mime_type, $properties['sources'] );
-				$this->assertArrayHasKey( 'filesize', $properties['sources'][ $mime_type ] );
-				$this->assertArrayHasKey( 'file', $properties['sources'][ $mime_type ] );
-				$this->assertArrayHasKey( 'source_url', $properties['sources'][ $mime_type ] );
-				$this->assertNotFalse( filter_var( $properties['sources'][ $mime_type ]['source_url'], FILTER_VALIDATE_URL ) );
-			}
-		}
-		$this->assertArrayNotHasKey( 'sources', $data['media_details'] );
-	}
 }
