When you look at the image below, whose face do you see? At normal screen viewing distance you should see the face of the great scientist Albert Einstein. Now squint your eyes or take a few steps back from the image. Does a certain Hollywood personality pop into view? The Marylin Monroe-Einstein hybrid image was created by Dr. Aude Oliva for the March 31st 2007 issue of New Scientist magazine.
It's not just a crafty illusion. This sort of image is being used as a tool to understand better how our brains process visual scenes. On the practical side, some companies are interested in using them to conceal information from unintended observers - or to create printed advertising that morphs before your eyes.
source : http://amazingillusions.blogspot.com/2007/04/marylin-monroe-einstein-illusion.html