First image (external) in "popular post"

Hi.

I have the popular post and I want add also an image.

I use this script to capture first image from a post:

function get_first_image() {
global $post, $posts;
$first_img = '';
ob_start();
ob_end_clean();
$output_img = preg_match_all('/<img.+src=[\'"]([^\'"]+)[\'"].*>/i', $post->post_content, $matches);
$first_img = $matches [1] [0];

if(empty($first_img)){ //Defines a default image
$first_img = "images/default.jpg";
}
return $first_img;
}

I want add the function “first_image” into this script:

if ($output) {
		foreach ($output as $line) {

		$hits = ($instance['show_hits']) ? ' ('.(int)$line->meta_value.')' : '';

	  	$out .=  '

<a title="'.str_replace("'","'", $line->post_title).'" href="'.get_permalink($line->ID).'">'.$line->post_title.'</a>

					<span class="most_and_least_read_posts_hits">'.$hits.'</span></div><!-- fine top_post -->';
		}
	} else {
		$out .= ''.__('No results available', 'least_read_posts');
	}
	return $out;
}