Open the admin/common/imageinfo.php file and change line 25 to be $info = array('"user_id":"' . [UserID] . '"'); replacing [UserID] with your PHP code.
Then open admin/js/manageimages.js and on line 215, add + '/' + image.user_id after where it says image.gallery_id
Give that a try and see if it works. Essentially you are adding a new javascript variable so the image path can be set correctly.
-justin