Hi Martin!
Why not include Alvaro Corugedo's script in v1.3
Image in Course Display for each course
http://moodle.org/mod/forum/discuss.php?d=4793
It is a nifty way to customize the Course descriptions on the category pages. It can be used to repeat an image to indicate the typle of course or even the instructor. Quick identification value.
Also, I think Alvaro is working on a script that will allow for different images depending on the Resource.
WP1