In law school, one of the very first things they teach you is that the law is not even close to black and white–it’s an interpretation of meanings and previous decisions. Thus, when someone asks “is this legal” lawyers have to do their best to figure out at what the courts will probably think, in this particular set of circumstances. Stating “This is THE law” is the equivalent of nailing jell-o to a board–it’s probably only going to hold true for an instant.
This sort of explains why you photographers so often hear things like “It’s better to get a release” rather than “Here are the exact rules for needing one.” It’s an attempt to give you the best chance at avoiding a law suit–not winning or losing one, just avoiding one altogether. Because law suits are expensive and sometimes, even when you are think you are safe, the case will go to trial (that is, the courts won’t dismiss it right off).
Like this one. This woman posted a video on YouTube of her kid dancing to a Prince recording. The record company is suing her for copyright infringement. Most people would have thought that had to be some kind of fair use, and the courts may interpreted it as such, but in the meantime, she and the record company are spending a lot of money to litigate the issue.
Moral? Use best practices and get your legal advice from a lawyer when it comes to your contracts, releases, etc. Don’t rely on advice from other photographers on forums for this stuff.