only other thing I can think of is to maybe have a small list of user bars that are already in a ftp folder they can chose from in a drop down to maybe use as a background. and possibly have it where say user 1 uploads a blank background it stores it in a folder so this way user 20 could possibly use that background also in the future. here is a few blank ones if you wish to do that.
http://www.userbars.us/categories.php?cat_id=2 a few other things maybe for a user to be able to chose different color scan lines, different color text and have a few different overlays in which there could be a drop down and show which one there using kinda like on here
http://userbarmaker.com/. last thing I could think of is some kinda hot link protection also.