This tool is called photoshop. Both you and I are already doing it; let's not make it easy for MORE people to horn in on the action eh?!
J/K, and I'd love to play with this... but I think Scaren is right, way down the 'to do' list. I would also say; if there are ever contests for this it should be players submitting maps and Devs voting on them. No player votes, period. Takes a lot of the politics out of voting polls and such, and Devs always have a better idea of where game SHOULD go than players, who tend to be more concerned with benefiting themselves.