Technically (under German law) any creation is automatically copyrighted the moment it's created. Whether US law says it wasn't is not relevant for a German cou

Technically (under German law) any creation is automatically copyrighted the moment it's created. Whether US law says it wasn't is not relevant for a German court. The chance of the creator suing is small but it's not zero. CC0 and the like carefully work around these laws (which exist in many countries beside Germany) by giving you a license to do anything with the work (while retaining copyright – but that's only a technical distinction). Of course one might argue that a US government worker implicitly gave up their rights in a similar way, but as far as I'm aware nobody looked into that yet.