Antique Tintype Mini Photo Frame

This beautiful picture frame was discovered inside a wooden jewellery box that was purchased at the auction. I fell in love with it without knowing anything about it except that it must be old. Have tried to research more online but I was not able to find out much - I guess I was missing the keywords.
The only thing that I can provide beside the photos that the backing feels and look like that is made out of some kind of leather
Measurements: 8.5cm x 10cm (3 1/4in x 3 7/8in)
I hope you like it as much as I do and maybe can help me out with my search.
Take care
Nena011