I am serious broken no with the surgery I have to do and moving. But as soon as I get some spare money (if I get) I will check it with a lawyer.
As I said, while I don't know of anyone specific in your area, I would be surprised if there were not a FREE legal advocacy group for artists in Germany that would have a lawyer who could answer this question for you, or maybe even have a pamphlet or guide that discusses this, because it would be a very common question. Or perhaps there is a professional association for photographers in Germany that would be willing to explain something like this, also for free. Here in the US we have the ASMP (American Society for Media Professionals, nee American Society of Magazine Photographers). I would be shocked if there isn't a DSMP equivalent. I'd post an inquiry about such organizations over on APHOG.de to see if someone can refer you to the proper groups.