Hmm, I guess this is something that should be mentioned in the rules of every sub-forum. For some reason, I only have a rule about images for the art forum.
Well then, how about this for an official ruling: It's fine to post "naughty" pics/videos if you do the following:
1. do not direct post them, but post them as links.
2. clearly label what the adult content of the image is.
Also, while nudity is fine, please no links to "extreme" content.