So, I saw a Tom Green video the other day, he walks into a pharmacy and awkwardly buys condoms. While this is mild compared to other things he's done, how does he get away with it?

You can't just broadcast video of people without their permission, even their voice and words, because those are considered to be their likeness.

Does it have something to do with the fact that he's in public?

Presumably he gets them to sign releases, but in certain situations (he pissed off a bunch of old people as a bingo-master once) I can't see why the people would sign a release.

I mean, suppose I'm taking video of my family trip to New York, and someone walks through the shot and I put the video on Youtube for the family to enjoy. Could the background-walking guy sue me for illegal use of his image?

So, anyone who understands the law in this particular field, it would be nice if you could clarify.