The illusion of sex « Best Visual Illusion of the Year Contest

[tamaranth]

The illusion of sex « Best Visual Illusion of the Year Contest
two faces are perceived as male and female. However, both faces are actually versions of the same androgynous face. One face was created by increasing the contrast of the androgynous face, while the other face was created by decreasing the contrast. The face with more contrast is perceived as female

Also worth checking out the 2009 finalists -- Illusion of the year. Some intriguing illustrations of visual phenomena.