from http://mathworld.wolfram.com/YoungGirl-OldWomanIllusion.html “ A famous perceptual illusion in which the brain switches between seeing a young girl and an old woman (or "wife" and "mother in law"). For many years, the creator of this figure was thought to be British cartoonist W. E. Hill, who published it in 1915 in Puck humor magazine, an American magazine inspired by the British magazine Punch. However, Hill almost certainly adapted the figure from an original concept that was popular throughout the world on trading and puzzle cards.”
