Over all the centuries of book production, artists have painted images on the cover and the spine and the inside pages, but artwork has been bestowed on another part of the book called the "fore-edge."
This is the area of the book you would see if you take the pages of the closed book and fan them out in one direction. The surface is composed of hundreds of tiny "steps" of individual pages spread out in series. When the book is closed normally, the edges of the book are simply colored with gold, and the painting disappears.
The art form reached its peak in England in the eighteenth and nineteenth centuries, as collectors hired painters to create these ingenious novelties. It's hard to track down the names of the individual artists because they generally didn't sign their work.