I guess we are lucky that the law in Germany doesn’t follow the the-camera-steals-your-soul-theory with regard to personal rights – i.e. taking a photo or filming in public is never (pretty much, the exception is stalking) illegal, personal rights of the photographed can only be violated by making the photos public (and the law has certain exceptions were making photos public is legal even without consent of all the photographed).
But it’s certainly true that the police can majorly inconvenience you. They can take your camera away and even though they have to give it back to you and are not allowed to delete anything that they can do that at all does suck. At least they cannot fine you or worse.
The most annoying thing is that many in the police seem to be unaware about the law. (They strangely never seem to have that problem when a law gives them more power.) They will lecture you on and on about personal rights even if those are irrelevant as long as you don’t plan to make the photos public. (And even if you, say, documented police brutality a newspaper could print the photo no problem, they would just have to pixelate faces.)