Yeah, there's a ton of programs out there that will merge two photos together to make them stereoscopic, provided you have two photos of the same thing with the camera panned slightly to either side. Thus, if you want to make something that doesn't have a sister photo stereoscopic, you have to alter the original to be what it would look like if the 'camera' jumped over to the side a few feet.
You do it by slicing up the image into a series of layers (I think this one had 10, which isn't very much at all) based on how 'deep' each part of the picture is. You then shift each layer to the right, moving the closest layers most, and the further ones least, or even shifting further ones to the left. Et voila! 3D image.