This is a replacement for the glass lampshades that are used in many bathrooms and ceiling fans. Usually they are connected by 3 small screws on a fan, or by a large nut that goes around the socket where the lightbulb screws in, and is easy to remove and replace. For bathroom fixtures I recommend only using one square image since you wont see the back side, but for ceiling fans, you can use 2-4 images on each.. whatever images your heart desires, and each can be different!
Its kind of hard to see the detail from a picture of a lithopane.. but the Wikipedia page really has some nice shots that show what its really all about.. I highly recommend you take a look! https://en.wikipedia.org/wiki/Lithophane