just remembered
I've got one in a book that turns black and white when you focus the right way. It helps by reinforcing the correct way of focusing on the image.
Another thing are [link|http://www.magiceye.com/advert4.htm|floaters]. If you look at the following image the right way, you'll see 7 apes - 5 apes in the middle will be 3D. These are easier to see than the hidden images, and once you get used to seeing these you'll be that much closer to seeing the hidden images.
[image|http://www.magiceye.com/images/apes2.jpg||||]
