[Plugin: Most And Least Read Posts Widget] Add first image for each most read post

Hi.
I want add the first image of a post in this plugin.

I use this script (in functions.php) for the first image:

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;
}

How can I add an image for each most read post?

http://wordpress.org/extend/plugins/most-and-least-read-posts-widget/