actually, unless its something nasty like porn(which i doubt it is lol) i personally dont think nudity should be hidden from minors(like extra percautions taken). i mean, everyone either has breats or a penis and everyone is naked under their clothes. seeing someone else isnt that much different then seeing yourself in a mirror.
There would be no male dangly bits (cropped out or shadowed), there may be woman boobs though, definitely some butts. But here is the thing, there would be the bondage thing and the suspension thing going on. Now that makes me more nervous than the nudes, that is why I think there should be a warning sign on it.
Lets not call it a warning. Lets call it information about the subject matter inside. There is a big difference, in my opinion, between art and porn. You are proposing what seems to me to be art and whether it is painted or photographed people should learn the difference.