Arthur C. Clarke and Isaac Asimov
An Extra Dimension

If you look at this image correctly, you might be able to see a 3D effect.

Now by "correctly" there's two ways. One is to look at the left and middle images with "cross-eyed" viewing. You cross your eyes and have the two images fuse into one (you will also see two other images on either side).

Or you can look at the center and right image with the "parallel" view. That is you focus your eyes to way beyond the image - like you're looking a point far behind the pictures - and you'll see the images fuse (and again you'll see images on either side as well. The center image should look 3D.

If you follow these instructions, the slight differences in the images should make Isaac look like he's a bit behind Arthur. If you do the reverse - parallel viewing for the left and center image and cross-eyed viewing for center and right image - it will look like Isaac's in front.

References

"How to View Without 3D Glasses", Donald Simanek, Lock Haven University.