@gdp @pratik @microlorian in Germany it's a bit different as far as I understand german law (aka I don't have a clue). On the one hand you are allowed to take pictures in public in almost all cases (with very few exceptions). On the other you have conflicting rights when you want to publish them. There's "freedom of art" vs. the "personal rights" or "the right to one's own image". As soon as you can identify a person on the picture it is not clear anymore and it becomes a legal case-by-case decision. So it's a grey area. If you publish it artful enough it should be ok. But what do I know.
In the end it seems to come down to: "Wo kein Kläger, da kein Richter." (Where there is no plaintiff, there is no judge).
So if you want to publish a photo with someone on it who can be identified, you'd be on the safe side to get consent to publish it.