Embossing then, its the same thing really. Isn't watermarks made by wire pressing on wet paper?
How do one goes about embossing a photographic print without damaging it as well?
The emulsion is a delicate thing and I fear that any press like contraption would be too much.
In all the history of photography, no one ever cared about this subject? I would think, a certain method would have been available since forever.