Limit uploading, only one kaleidoscopic wallpaper per day, maybe less. So the uploader has to choose the best one but is still allowed to submit them.
Kaleidoscopic wallpapers (or overused types in general) have to be marked when uploading, a single tick is enough. Not marking correctly leads to content removal. Trying to upload two "limited" wallpapers will result in an error (try again tommorow)