http://i47.photobucket.com/albums/f194/vdlsrjgfas/dog.jpg

Don't look at one part, look at all of it.
Blur your eyes a little and the 3D image becomes crystal clear.

Once you're locked in, you can move your head left and right slightly and the dog moves in this 3d 'world'

doesnt work for me.

better ones...

http://i40.tinypic.com/ipqz52.jpg

this one still amazes me...

http://www.ratemyeverything.net/image/791/0/Incredible_Color_Optical_Illusion.ashx

Squares A and B are the same colour.