Thatcher Illusion

The Thatcher Illusion was created in 1980 by an individual called Peter Thompson, and it only got that name because he first applied the technique to a picture of Margaret Thatcher.  Thompson basically inverted the eyes and mouth of an image a smiling Thatcher and then turned the whole picture upside down.  The illusion works because it is hard to notice that there is anything wrong with the picture. To the eye the smile still looks like a smile.