I agree on keeping the author of the art secret until voting has ended, if possible. What also might be a good idea, is to ignore the highest 20 and the lowest 20 votes (number may vary), to ensure only fair votes will be counted.

Maybe we could just email our submission to a certain email address, and when the contest closes someone makes a voting thread, or a poll of some sort. That would lose the forum effect though, so you won't get as much critique. Then again, one could always discuss the contest afterwards.