Ugh... this is getting too complicated. As a general guideline, how about if someone has a bunch of wallpapers of a size that doesn't seem too odd, they post them in their own separate forum. If a person only has a few pics of a type that doesn't already have their own forum, they post it here; slightly disproportional wallpapers would also go here as well (lets say, off by a few pixels on a side). People who don't want to check pixel sizes of multiple wallpapers will probably post them here anyways, so why make the system more complicated if it will only become increasingly difficult to check & police?
Does this sound reasonable to you guys? Other suggestions?