I'm an American living in Berlin. I do a fair of amount of photography here and have some perspective to offer. An important part of the privacy laws is the prohibition on sharing on social media. Even if you can legally take a photo, sharing someone's likeness on Instagram is not allowed without permission and is actionable in court. Newspapers here take care to share different images on social media than they do on their own websites. It's common to see faces blurred on Twitter or Instagram if they even share it.

Even if it is legal, Germans are quick to confront people taking pictures. They will get in your face and yell at you about it and tell you to delete images. It rarely gets physical, if ever, but up to you if you want to deal with all that. This happened to me twice when I was taking photos of crowds, once at a flea market and the other outside a subway station on the street.

Don't even think of bringing a drone. They hate them and the restrictions are severe. I have all the required licensing and insurance and still can't fly in most of the city.

You also need to be aware of cultural differences within the international community. Berlin has a large Arab population and their tolerance of photography seems to be very different, especially if women or children are included. Also, some Slavs and Eastern Europeans are extremely suspicious of people taking pictures of strangers. Be warned.

Don't take pictures on the trains or subways, even selfies. I have seen some people get angry about that.