Now, now Exapno and drhess, chill. You’re both IMHO kinda right. In my experience (as a lawyer) there are two things that get confused when people talk about the law.
1/ There’s the black (or usually somewhat gray) letter of the law.
2/ There’s the practical upshot.
The one sometimes doesn’t directly reflect the other. They are both, in a sense, relevant to legal prudence.
In this instance, the (as mazinger_z’s cite makes apparent) dark gray letter of the law is, I think, what Exapno says.
However, while it may be that “the courts generally agree that anything visible in a public place can be recorded”, what is the practical upshot? Well, let’s look at it from the point of view of a publisher buying a photograph off a photographer for commercial use.
Firstly, they don’t know what you actually did to get the photo. That is to say, if the publisher is sued they have potential evidential problems, regardless of what actually happened.
Secondly, there is potentially a world of pain for the publisher as a consequence of the words “gray” and “generally” as used above. In other words, the publisher may incur costs and delays due to someone suing them on uncertain or even insubstantial grounds, quite regardless of merit.
So while in one sense it is correct to say that (per Exapno) “You can take pictures of anybody, you can publish pictures of anybody, with or without their permission or even over their objections” it is also correct to say that (per drhess) arguably the legally prudent thing to do would be to get a release if at all possible, if you have any intention of publishing.
And I’m not your lawyer, and I don’t practice in your jurisdiction and I wouldn’t act for you even if I did (so there), and I’m not in my field and anyone who relied on this advice would be silly.