Is that Einstein or Harry Potter? It depends on how far you're standing from the image! Jeremiah Owyang of Web Strategy blog saw this hybrid image optical illusion at the MIT museum in Cambridge:
... at first I didn’t understand how it worked. Later as I walked to the end of the room, I saw that someone had switched the drawings!
As I walked closer, they magically reverted back to Albert Einstein.
Link (See for yourself: small version of the pic, large version) - via Blog Hogwarts, Thanks Alejandro Martinez!
See also: Dr. Angry and Mr. Smiles