The two pictures are a stereo pair. They work like the "magic eye" pictures from a few years back or the stereograms seen in organic chemistry textbooks. Relax your focus as if you were looking into the distance, you should be seeing double! Instead of two images of me there should appear to be four. What you need to do is to get the right-hand image of the left head to overlap with the left-hand picture of the right head. When this happens you should see three images with the one in the middle appearing to be in 3-d.

In short - by accident. I was having a passport photo done in "Max Speilmans" in Withington. The four photos were done using a Polaroid camera instead of the usual booth. The photos appeared all on one sheet which was cut into four later. I noticed when the photos developed that the pictures didn't look quite the same. Then I realised the four photos were produced by using a camera with four lens. Because each lens took a photo from a slightly different position each resulting photo showed a slightly different angle.

It just happend that the distance between the lens on the right and those on the left were similar to the distance between my eyes, so the images recorded were different to those by my left and right eye. So, if one photo from the left-hand lens and one from the right were placed close together I could use the method above to recombine the images to produce the 3-d image.