My students have been spending lots of time looking at this picture of Einstein/Monroe. Up close, it looks like Einstein. Back up and it looks like Monroe.
Here is a short piece on Botjunkie that describes why this happens and how it's important in designing robots to see.
Also, here is a whole gallery of these images, including a few movies demonstrating the effect. I fear that if I show these to my students, they will be lost to me for hours.
[Image: Captured from Botjunkie: http://www.botjunkie.com/2009/05/01/albert-einstein-marylin-monroe-hybrid-may-help-robots-see-like-humans/