Artists fascinated by optical illusions and keen to explore the limits of painting have long indulged in visual puzzles and changing perspectives. Playing on the ambiguity of double images, which change with the observer s point of view, many painters have covered their tracks and introduced several meanings, often hidden, in images that can be read in multiple ways. They did so for fun, but also to give their works moral or symbolic meaning, or even religious, political or sexual connotations.Available in french and english.