Flickr does not specialize in the domain, but tolerates the practice under some conditions; so if you use Flickr make sure all of adult photographs in your stream are flagged as 'restricted'. Also, do know that if you post such images, your stream cannot be found in search as it will be flagged as NIPSA Not In Public Search Areas and as 'unsafe', however there still are photographs of this genre in flickr, some of them artistic, others less so. The key here is to flag your photographs correctly or your account will be suspended. Unfortunately I do not know of other photo sharing sites for this particular genre.