Meaning of fore-edge painting

fore'-edge paint"ing

Pronunciation: (fôr'ej", fōr'-), [key]
  1. a technique of painting a picture on the fore edge of a book, often in such a manner that only when the pages are slightly fanned the picture is revealed.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.