Perhaps in addition to the generic "wallpaper search", a function could be added to further assist in locating images. Other sites already have this functionality, and if I'm not mistaken, the search, or "key" words are selected by the artists themselves.

Take, as an example, a search someone asked about recently. They were looking for shark wallpapers. Now let's say someone had one, but the word "shark" appeared in neither the title, not the description. Instead, they called it...oh, let's say "terror of the sea" and said, "wouldn't want to get this close again". A "wallpaper search would fly right by this image. A keyword search, where the artist included, say, "underwater", "shark", etc. would be a bit more specific.