Fore-Edge Paintings in 19th Century Books

Fore-edge painting, which is believed to date back as early as the 1650s, is a way of hiding a painting on the edge of a book so that it can only be seen when the pages are fanned out. There are even books that have double fore-edge paintings, where a different image can be seen by flipping the book over and fanning the pages in the opposite direction.

(via This is Colossal)