We chose to create depth-of-field by having our raytracer (optionally) generate a stereographic pair of images.  The artifact you see is one such pair.  The large sphere in the middle of the image is meant to look like glass, and the cylinder it rests upon is chrome.  There are three colored glass marbles, and you can see that their shadows bear the same color.  Note that the blue shadow isn't very blue because it falls on a yellow surface.  On the right there is a spotlight mounted on a tripod.  The only other light source is a directional light meant to represent the sun.  The background image is set at infinity, and is wrapped around the sides so that the reflections will look decent.  To see the image in 3D, allow your ciliary muscles to relax until the dunes in the background overlap.  Now look at the foreground, and your ciliary muscles should automatically contract slightly to bring whatever object you are looking at into focus.  NOTE: to see this well without having to strain your eyes, resize the image so that its width is slightly less than twice the distance between your eyes.