Add this on your search.php

$search = $wp_query->get('s');
	$keywords = preg_replace('/\+/',' ',$search);
	if (function_exists ('ngg_get_search_pictures')) {  // function from functions.php
		$nggpictures = ngg_get_search_pictures($keywords, ''); // put the number of pictures by row you want, if you don't want "4"

		if ($nggpictures) {
			echo "
Bilder

";
			echo $nggpictures;
		}
	}

Add this to your functions.php

/**
** Function to do searchs on gallery pics from NextGen Gallery plugin
**
** @keywords		keywords, usually gave by the standard search query from wordpress
** @numberPicCol	number of pic by row. If null, it takes 4 by default
*/
function ngg_get_search_pictures ($keywords, $numberPicRow = NULL) {
	global $wpdb;
	$count=1;
	if (!$numberPicRow) { $numberPicRow = "4"; }

	$nngquery = $wpdb->prepare( "
				SELECT pid,description,alttext
				FROM " .$wpdb->prefix. "ngg_pictures
				WHERE MATCH (description, filename, alttext) AGAINST (%s IN BOOLEAN MODE)
				AND exclude != 1
				","*".$keywords."*");

	$pictures = $wpdb->get_results($nngquery, ARRAY_A);

	if ($pictures) foreach($pictures as $pic) { 

		$out .= '

';
		$out .=  '

';
		$out .=  "\n"; 

		if ($count == 0) {
			$out .= "";
		}

		++$count;
		$count%=$numberPicRow;
	}
	return $out;
};