The Illusion of Sex Change

Both the faces are versions of the same androgynous face (neither male, nor female). 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, while the face with less contrast is perceived as male.
Check it out here: http://www.moillusions.com/2009/05/illusion-of-sex-change.html