Index: src/wp-includes/widgets/class-wp-widget-recent-posts.php
===================================================================
--- src/wp-includes/widgets/class-wp-widget-recent-posts.php	(revision 40304)
+++ src/wp-includes/widgets/class-wp-widget-recent-posts.php	(working copy)
@@ -56,6 +56,7 @@
 		if ( ! $number )
 			$number = 5;
 		$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.
@@ -82,6 +83,9 @@
 		<ul>
 		<?php while ( $r->have_posts() ) : $r->the_post(); ?>
 			<li>
+			<?php if ( $show_thumbnail && has_post_thumbnail() ) :
+				the_post_thumbnail( 'thumbnail' );
+			endif; ?>
 				<a href="<?php the_permalink(); ?>"><?php get_the_title() ? the_title() : the_ID(); ?></a>
 			<?php if ( $show_date ) : ?>
 				<span class="post-date"><?php echo get_the_date(); ?></span>
@@ -113,6 +117,7 @@
 		$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;
 	}
 
@@ -128,9 +133,10 @@
 		$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' ); ?>" placeholder="<?php esc_attr_e( 'Recent Posts' ); ?>" type="text" value="<?php echo $title; ?>" /></p>
+		<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>
 
 		<p><label for="<?php echo $this->get_field_id( 'number' ); ?>"><?php _e( 'Number of posts to show:' ); ?></label>
 		<input class="tiny-text" id="<?php echo $this->get_field_id( 'number' ); ?>" name="<?php echo $this->get_field_name( 'number' ); ?>" type="number" step="1" min="1" value="<?php echo $number; ?>" size="3" /></p>
@@ -137,6 +143,9 @@
 
 		<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
 	}
 }