This is like a double forgotten bookmark. Color photo, 4 inches by 6 inches. Writing on reverse:
This photo was found in 'Ulysses' on top
Found in (wait for it) "Textbook of Dental Radiology" by Olaf E. Langland. Charles C. Thomas Publisher, 1984.
So... Someone else found this photo in a book (Ulysses) and thought enough to note the occasion. There were no copies of Ulysses in this particular batch of books I was sorting, so this one will have to remain a mystery.