santasser
I've looked around but nothing is clearly public domain.
In my opinion basically all of them, since they're hundreds of years old. Only the changes made to a work can be copyrighted. The trick is finding the originals, or scans made by libraries or museums for the purpose of public research. A photograph or scan of a work that is in public domain can't be copyrighted, but if I'm not mistaken color corrections can be.
I'm pretty sure not all of them are in public domain. For instance if you have done a redrawing.