Index: src/wp-includes/widgets/class-wp-widget-recent-posts.php
===================================================================
--- src/wp-includes/widgets/class-wp-widget-recent-posts.php	(revision 43660)
+++ src/wp-includes/widgets/class-wp-widget-recent-posts.php	(working copy)
@@ -56,6 +56,8 @@
 		}
 		$show_date = isset( $instance['show_date'] ) ? $instance['show_date'] : false;
 
+		$show_thumbnail = isset( $instance['show_thumbnail'] ) ? $instance['show_thumbnail'] : false;
+
 		/**
 		 * Filters the arguments for the Recent Posts widget.
 		 *
@@ -97,6 +99,11 @@
 				$title      = ( ! empty( $post_title ) ) ? $post_title : __( '(no title)' );
 				?>
 				<li>
+					<?php
+					if ( $show_thumbnail && has_post_thumbnail( $recent_post->ID ) ) :
+						echo wp_get_attachment_image( get_post_thumbnail_id( $recent_post->ID ) );
+					endif;
+					?>
 					<a href="<?php the_permalink( $recent_post->ID ); ?>"><?php echo $title; ?></a>
 					<?php if ( $show_date ) : ?>
 						<span class="post-date"><?php echo get_the_date( '', $recent_post->ID ); ?></span>
@@ -119,10 +126,11 @@
 	 * @return array Updated settings to save.
 	 */
 	public function update( $new_instance, $old_instance ) {
-		$instance              = $old_instance;
-		$instance['title']     = sanitize_text_field( $new_instance['title'] );
-		$instance['number']    = (int) $new_instance['number'];
-		$instance['show_date'] = isset( $new_instance['show_date'] ) ? (bool) $new_instance['show_date'] : false;
+		$instance                   = $old_instance;
+		$instance['title']          = sanitize_text_field( $new_instance['title'] );
+		$instance['number']         = (int) $new_instance['number'];
+		$instance['show_date']      = isset( $new_instance['show_date'] ) ? (bool) $new_instance['show_date'] : false;
+		$instance['show_thumbnail'] = isset( $new_instance['show_thumbnail'] ) ? (bool) $new_instance['show_thumbnail'] : false;
 		return $instance;
 	}
 
@@ -134,9 +142,10 @@
 	 * @param array $instance Current settings.
 	 */
 	public function form( $instance ) {
-		$title     = isset( $instance['title'] ) ? esc_attr( $instance['title'] ) : '';
-		$number    = isset( $instance['number'] ) ? absint( $instance['number'] ) : 5;
-		$show_date = isset( $instance['show_date'] ) ? (bool) $instance['show_date'] : false;
+		$title          = isset( $instance['title'] ) ? esc_attr( $instance['title'] ) : '';
+		$number         = isset( $instance['number'] ) ? absint( $instance['number'] ) : 5;
+		$show_date      = isset( $instance['show_date'] ) ? (bool) $instance['show_date'] : false;
+		$show_thumbnail = isset( $instance['show_thumbnail'] ) ? (bool) $instance['show_thumbnail'] : false;
 		?>
 		<p><label for="<?php echo $this->get_field_id( 'title' ); ?>"><?php _e( 'Title:' ); ?></label>
 		<input class="widefat" id="<?php echo $this->get_field_id( 'title' ); ?>" name="<?php echo $this->get_field_name( 'title' ); ?>" type="text" value="<?php echo $title; ?>" /></p>
@@ -146,6 +155,9 @@
 
 		<p><input class="checkbox" type="checkbox"<?php checked( $show_date ); ?> id="<?php echo $this->get_field_id( 'show_date' ); ?>" name="<?php echo $this->get_field_name( 'show_date' ); ?>" />
 		<label for="<?php echo $this->get_field_id( 'show_date' ); ?>"><?php _e( 'Display post date?' ); ?></label></p>
+
+		<p><input class="checkbox" type="checkbox"<?php checked( $show_thumbnail ); ?> id="<?php echo $this->get_field_id( 'show_thumbnail' ); ?>" name="<?php echo $this->get_field_name( 'show_thumbnail' ); ?>" />
+		<label for="<?php echo $this->get_field_id( 'show_thumbnail' ); ?>"><?php _e( 'Display post thumbnail?' ); ?></label></p>
 		<?php
 	}
 }