There is a process that allows you to make photographs directly on a piece
of silver: daguerreotype.
The image is extremely fragile however and would have to be protected
behind glass in a locket. I just bought one of those, made ca. 1845, a few
weeks ago.
I'm sure you have my Encyclopedia or Printing, etc. Check Etched
Daguerreotype, Electro Engraving, Electro Etching, etc.
Some people have successfully used laser systems to etched photographic
images on just about anything. I have received specimens etched on
plexiglass, wood, and even cement blocks. They can be used as a final image
or as intaglio plates, etc.
Luis Nadeau
Fredericton, NB, Canada