tcrsavage · July 17, 2013 02:36 · Jul 17, 2013
diff --git a/gistfile1.php b/gistfile1.php
@@ -0,0 +1,14 @@
+//If no post thumbnail exists, get the first image in the post and return that instead
+add_filter( 'post_thumbnail_html', function( $html, $post_id, $post_thumbnail_id, $size, $attr  ) {
+
+    if ( $html )
+		return $html;
+
+	$found = preg_match( '/<img.+?class=\".+?([0-9]+).*\/>/', get_post( $post_id )->post_content, $matches );
+
+	if ( $found )
+		$html = wp_get_attachment_image( end( $matches ), $size, false, $attr );
+
+	return $html;
+
+}, 10, 5 );