A little test to exercise your eyes

Albert or Marilyn?

This picture is a well known optical illusion. It is both a picture of Albert Einstein and Marilyn Monroe depending on how far away the viewer stands from the picture. You can try it yourself: if you get back from your screen, you will see Marilyn Monroe slowly emerging.
When looking at a person from about fifteen feet, the face is still recognisable but details like eyebrow hairs, wrinkles and small moles are much less visible. This is why the photograph looks like a youngish Marilyn Monroe at a distance – we see no wrinkles or blemishes. Close up, we see various lines denoting Einstein’s eyebrows, nose and moustache and wrinkles, especially about the eyes.
If you still can't quite see the transformation, try squinting at the image... Marilyn should appear as if by magic! 
I actually have no idea how this really works or indeed who thought to construct it in the first place - it's just amazing though. Any one else have similar optical illusions?
John W.