I dont wanna say what is right or wrong... but when someone be part of a professional porn movie i assume there is a contract, and the person will no longer control the porn movie made, where the person is completly naked - even on fetish scenes. Doing nudes and giving the rights (in good will) to another person could be something similar - of course in moderate boundaries. Make sense?
Correct, porn models are treated much like any other actor or model and have a contract that gives the producer the right to the images or video of them.
The same kind of thing is not viable in with amateur "modelling" as the contracts are quite complex and being legal documents subject to the law of the country. As sites like this are very much international in nature contracts are unlikely to give any protection to either the model or the poster, the best you can do is hold to a reasonable code of conduct.
As far as we are concerned here at Kink Talk the biggest issue is when the photos include a face as this compromises identity which is why we have had to tighten our rules. Including a hand written consent note is as close as we can get to having some sort of proof that the poster is acting in good faith.
As far as the reality of posting your photos online goes, as I have warned previously once they are posted, even for just a few minutes they could be on the web forever. There is simply no way to track where they go if someone downloads them and posts them on other forums, within days there could be hundreds or thousands of copies in circulation.
Because of the very real threat of legal action with regards to revenge porn we cannot take chances, this means if we have any doubt we will take down an album without notice.