I saw the same thing I saw when I looked at the original image, just inverted. It's not really an optical illusion, though--more like persistence of vision. Related to the spots you get after looking at a bright light. There are some better examples of optical illusions
here.
Besides, whaddya mean "a perfect image of Jesus"? Nobody knows what he looked like, or even that he existed. We know what various artists thought he might have looked like, though, assuming he did exist.
Torben