Index: wp-content/themes/twentyten/functions.php
===================================================================
--- wp-content/themes/twentyten/functions.php	(revision 23798)
+++ wp-content/themes/twentyten/functions.php	(working copy)
@@ -514,3 +514,44 @@
 	);
 }
 endif;
+
+/**
+ * Finds galleries for a post, then counts the total number of images and finds
+ * the first image in the gallery, for display on index/archive/search views.
+ *
+ * @uses get_post_galleries() first, if available. Falls back to shortcode parsing,
+ * then as last option uses a get_posts() call.
+ *
+ * @since Twenty Ten 1.6.
+ *
+ * @return mixed Boolean on empty result, array of image IDs if successful.
+ */
+function twentyten_get_gallery_images() {
+	$images = false;
+
+	if ( function_exists( 'get_post_gallery_images' ) ) {
+		$galleries = get_post_galleries();
+		if ( isset( $galleries[0]['ids'] ) )
+		 	$images = explode( ',', $galleries[0]['ids'] );
+	} else {
+		$pattern = get_shortcode_regex();
+		preg_match( "/$pattern/s", get_the_content(), $match );
+		$atts = shortcode_parse_atts( $match[3] );
+		if ( isset( $atts['ids'] ) )
+			$images = explode( ',', $atts['ids'] );
+	}
+
+	if ( ! $images ) {
+		$images = get_posts( array(
+			'fields'         => 'ids',
+			'numberposts'    => 999,
+			'order'          => 'ASC',
+			'orderby'        => 'menu_order',
+			'post_mime_type' => 'image',
+			'post_parent'    => get_the_ID(),
+			'post_type'      => 'attachment',
+		) );
+	}
+
+	return $images;
+}
Index: wp-content/themes/twentyten/loop.php
===================================================================
--- wp-content/themes/twentyten/loop.php	(revision 23798)
+++ wp-content/themes/twentyten/loop.php	(working copy)
@@ -70,20 +70,19 @@
 				<?php the_content(); ?>
 <?php else : ?>
 				<?php
-					$images = get_children( array( 'post_parent' => $post->ID, 'post_type' => 'attachment', 'post_mime_type' => 'image', 'orderby' => 'menu_order', 'order' => 'ASC', 'numberposts' => 999 ) );
+					$images = twentyten_get_gallery_images();
 					if ( $images ) :
 						$total_images = count( $images );
 						$image = array_shift( $images );
-						$image_img_tag = wp_get_attachment_image( $image->ID, 'thumbnail' );
 				?>
 						<div class="gallery-thumb">
-							<a class="size-thumbnail" href="<?php the_permalink(); ?>"><?php echo $image_img_tag; ?></a>
+							<a class="size-thumbnail" href="<?php the_permalink(); ?>"><?php echo wp_get_attachment_image( $image, 'thumbnail' ); ?></a>
 						</div><!-- .gallery-thumb -->
 						<p><em><?php printf( _n( 'This gallery contains <a %1$s>%2$s photo</a>.', 'This gallery contains <a %1$s>%2$s photos</a>.', $total_images, 'twentyten' ),
 								'href="' . get_permalink() . '" title="' . esc_attr( sprintf( __( 'Permalink to %s', 'twentyten' ), the_title_attribute( 'echo=0' ) ) ) . '" rel="bookmark"',
 								number_format_i18n( $total_images )
 							); ?></em></p>
-				<?php endif; ?>
+				<?php endif; // end twentyten_get_gallery_images() check ?>
 						<?php the_excerpt(); ?>
 <?php endif; ?>
 			</div><!-- .entry-content -->