[lucb1e]

> if the subject is very familiar to you.

Fair enough, if you know what someone wears, their exact skin color, build, and perhaps even the place they are in, then sure, blacking out the face (or changing it for that matter) won't help. I guess I agree that this is more common than the authors make it sound (it's indeed not 100% guaranteed absolutely anonymous always ever, as they put it). But I do have to say, this is about as good as blacking out the face completely and a lot less obnoxious.

> The picture of Obama and Trump is clearly recognizable

You sure? If I show this picture in isolation to someone https://snipboard.io/VjwEc1.jpg I'm not sure that they will say it's Obama. Not sure there is a politically correct way of saying this, but there aren't that many people that are well-known by billions with that skin tone and in a suit, so of course if you ask them "the face was changed, who is this?" they can do a lucky guess for Obama because that's the only guessable possibility.