I think I found your answer - they are called Stanhopes first produced in the second half of the 19th century,are small, novelty mementos that contain a miniature peephole revealing a "mystery" photograph. Charles Stanhope British politician & scientist (1735-1861) who invented a uniquely powerful magnifying lens, achieving enlargements previously only possible with a microscope are who they are named after. If more info is needed I will be happy to help apparently these are hidden in objects such as perfume bottles they fitted them into the hinges, , sewing accessories,dip pens etc. plastic Stanhopes were produced after the 1920s.