Ban the Ass!
Can someone Ban bum/ass pics please its probably more offensive than penis pics, Unless they are gym freaks its never going to look good. Just makes you want to Vom! Pretty sure many agree with me on that as someone posted a post yesterday saying as much.
Rather than simply banning them, why not incorporate the ability to tag into the website. Include a mandatory requirement for a photo to be tagged when uploaded via a drop-down menu with a set choice of tags. (and yes this would rely on a certain amount of honesty on the part of the uploader)
This tag could also be checked when the photo is assessed by an admin to ensure it is accurate, and changed it if it is not. If the same uploader consistently uses an incorrect tag to dodge the system they could be penalised by not being allowed to upload photos for a given amount of time.
You then give the user the ability to choose which tags (and as such, type of photos) are visible to them in their settings so they can screen out what they find offensive or simply don't want.