Jason Kottke's posted an amazing primer on rolling your own stereoscopic images with a digital camera and some image-editing software. Possum, my high-school roommate was obsessed with stereoscopes and three-d (part of a lifelong project to write stereoscopic software to help people understand how to visualize n-dimensional space in three dimensions), and would build his own by drawing two nearly identical images and sticking them on the ends of paper-towel rolls, then putting the rolls up to his eyes and unfocusing his vision until the image converged. It all went great until one day, he decided to try to train his eyes to move independently by slowly moving the tubes apart, while keeping the image converged. Luckily, he stopped before he did any permanent damage.
Stereo photography turns out to be fairly easy to do if you're not concerned with exact results, even if you only have one camera. Choose an appropriate scene and photograph it from two different positions a small distance apart, making sure to keep the camera as horizontal as possible. That distance depends on distance between the camera and the scene, but for most pictures, an inch or two of separation between camera positions is sufficient. For the Lisa Simpson image, the figurines were about two feet away and I moved the camera only about an inch between shots. Make sure you keep track of which is the left most photo and right most photo. That'll be important when preparing the images for viewing.
(Thanks, Rob!)
