Wow, that’s a zealous printer! I’ve never heard of a printer turning down an image on copyright grounds. It is fair in a sense however, I guess.
The simple way is to send them an email detailing what prints they’re allowed to make, so if ever there is a an issue they can present the Copy Right they purchased. You could print up the letter yourself and sign it for them if you wanted them to have a harder copy. That’s assuming removing the copyright info and watermarks is out of the question. If you don’t mind removing them, it’s an obvious fix.
I’m a little uncertain on this issue, but there are ways to protect files from printing (and other forms of copying) which basically makes it impossible to print. I doubt your images are protected this way because I doubt one could protect their files that way and not know about it.
From a legal standpoint I would be curious to know wether the printer themselves would be liable for damages when printing the material provided by the customer. I sincerely doubt that. Leaving the burden on the printer to verify copyrights on everything they print is a bit of a stretch imho. That however is besides the point.
