Thank you KC, interesting resource!
Ipcress, it has not been appraised, but I had a look inside myself. The note was also inside, not visible when the frame is closed. It is painted on ivory, but as I have learned now, they printed photos on ivory as a base for miniature paintings at least from the 1860s, so still it could be the case. I tried to make a detail picture of the face, are there any signs that make you sure that it is a touched up photo? I am not interested in it's value, just trying to research it out of interest...
Mat