[Plugin: IMAGE EXTRACTOR] changing to category pages

is there a way to alter it so it extracts image from the category page instead of the post so I’ll have the same image for the post excerpt on the front page and not have to keep adding the same image for every post in that category. Just want to know how to extract images from category page instead of the post, I use this code to display images in the category page.

<?php
$this_category = get_category($cat);
echo '<img src="http://mysite.net/images/wpaper/'. $this_category->cat_ID .'.jpg" alt="'. $this_category->cat_name .'" />';
?>

http://wordpress.org/extend/plugins/image-extractor/