Index: src/wp-includes/post-thumbnail-template.php
===================================================================
--- src/wp-includes/post-thumbnail-template.php	(revision 44537)
+++ src/wp-includes/post-thumbnail-template.php	(working copy)
@@ -23,7 +23,19 @@
  * @return bool Whether the post has an image attached.
  */
 function has_post_thumbnail( $post = null ) {
-	return (bool) get_post_thumbnail_id( $post );
+	$thumbnail_id  = get_post_thumbnail_id( $post );
+	$has_thumbnail = (bool) $thumbnail_id;
+
+	/**
+	 * Filters whether a post has a post thumbnail.
+	 *
+	 * @since 5.1.0
+	 *
+	 * @param bool             $has_thumbnail true if the post has a post thumbnail, otherwise false.
+	 * @param int|WP_Post|null $post          Post ID or WP_Post object. Default is global `$post`.
+	 * @param int|string       $thumbnail_id  Post thumbnail ID or empty string.
+	 */
+	return (bool) apply_filters( 'has_post_thumbnail', $has_thumbnail, $post, $thumbnail_id );
 }
 
 /**