You know, there's a site called HentaiPalm.com. The forums are totally free, and you can upload and attach up to 10 pictures per post. The site is really fast, and there are more pictures than even here, I think.
Donations are appreciated, and there WAS one point where the forums were on the verge of closing down because of too few donations, when the site owner's wife recently had a kid and they couldn't possibly pay for both.
But in general, the guy runs the forums out of the kindness of his heart.
Not saying that the site owner here needs to do so much as well, but I'm just saying it's possible. No one has answered in this fashion yet, but just to catch it ahead of time, anyone saying that completely free forums are totally stupid, impossible, and completely out of the question, is flat-out wrong.
EDIT: Oh yeah, there aren't any ads there either.