nude photographs of kids online, not porn of course, is legal. Some of the sites will make you very mad though so don’t look for them.
Why would you say that? Try posting a photo of a nude child and see how quick you go to jail if caught.
A large percentage of these photos are likely to fall under the "lascivious exhibition" and/or "masturbation" criteria, given the circumstances under which they were taken.
Often it is a matter of prosecutorial discretion, which has been abused before.
As more and more of this garbage enters circulation, it becomes inevitable that CP will show up on secondhand/refurb phones, memory cards, hard drives, ipods, and so forth. A lot of innocent people will unwittingly come into possession of prohibited images, while at the same time the sickos and perverts will have plausible deniability because "it's everywhere now." Not a good situation at all.