If you do not have a model release from the subjects of the picture you are playing with fire. There is no "implied consent" in a court, you either have paper or you don't. If I take a picture of my wife and publish it without a release, I will lose, hands down.
There are several things to consider here. Forget "the law", it is more important WHAT A JURY will think. In the above mentioned case, I bet most juries would think I am an ASS and rule in favor of my wife.
Second, consider costs. HOW much IS IT WORTH to you to go to court to win? One case could cost you in the tens of thousands of dollars, however, it could cost the person suing you the same.
As far as 2257, DO YOU want to be a test case? If not, I suggest you keep everything in line, so even if your model is barley nude keep the appropriate records; that way you cannot lose.
You can do whatever you want to do, but at least weigh consequenses. May people push the limits of copyright, 2257, etc, and make GOOD money doing so, however, they might end up in jail some day. I, myself, do not want to be Mike Tyson's bitch
