|Step away from the screen (or squint)
and you will see Marilyn Monroe.
This type of image is called a hybrid image. This one was developed by Aude Oliva, Antonio Torralba and Philippe G. Schyns.
Here’s a website about them>>
A slideshow (careful – it opens a PDF file directly)>>
A technical article (again, opens a PDF)>>
See Eight Einsteins at MIT>>
And if you can’t bother to actually move away from the screen, watch this: