Are you familiar with this site: ?

It might be worth contacting its owner and asking what issues have arisen and how they were handled. He seems to have been doing this for a while.

My understanding is that even if an owner came forth and could establish copyright ownership, they could enjoin further use but only recover the amount of actual losses suffered, which in this case would be zero. It would be nice if someone knowledgeable could chime in on legalities here.