I am unaware of the specific law in Germany, but the way this kind of thing usually works in much of the world is that a judge or jury decides what the photo is

I am unaware of the specific law in Germany, but the way this kind of thing usually works in much of the world is that a judge or jury decides what the photo is "of" after being apprised of the relevant context. There are a lot of laws that deal with intent; the processes for this is pretty well-worn.