My avatar eyeball? Or my two eyeballs?

I have been doing these for about 15 years so I can see them out of the corner of my eyes, literally. As long as I can see the image with both eyes I can see the hidden image.

Your technique with the fingers is a good one.

What I always tell people who say they can never see stereograms, is get as close to the image as possible, your vision will be blurry. Try to maintain that blurry vision and DO NOT focus on the image. Move very slowly away from the image (or move the image slowly away from you). You should start to get a feeling of 3D depth. If so, keep the blurry focus and see if the image becomes more clear.

It is a lot harder to see these images reduced down to this size because the actual image is 20 x 16.