If people were born with only one eye, would seeing make any difference? Depth is perceived by the human brain by comparing two different images that the eyes send to it. Since people have two eyes that are spaced from each other, the things they see would make slight differences. These differences allow people to perceive if an object is near or far. So if people were born with only one eye, that would have probably warped their perception of the relation of things and you'd find them stubbing their toes or bumping into things, and being as incurably clumsy as a man in a blindfold.
A digital 3D photo maker works the same way as the eyes. Since the eyes form a triangle together with the subject, stereoscopic digital photography was developed by forming a triangle with the camera, hence 3D cameras are given two lenses.
When trying to create 3D images with a single lens camera, the trick is to almost replicate the first photo with just a few differences. This means that when you take the photo, you move the camera a bit to the left or to the right to try to get a similar photo.
When choosing what to shoot, try considering the distance of your subject to the background and decide if the 3D photo would help it “stand out.” If you have a single lens camera, then choosing subjects that move around may not be ideal.
Viewing 3D photos can be a bit tricky. Unless your camera or computer screen was specially designed to merge 3D images, you'll just get two different photographs of the same scenery. So, using 3D photo viewers would be the ideal way of viewing 3D photos. These viewers let you peek into binocular-like objects where the two images are simultaneously sent and processed by the brain. Since it creates a faux “triangle” from the eyes and the subject, the brain is tricked into thinking that there is depth.
Nowadays, cameras are also able to take 3D videos that make the action “pop out” into reality. Gone are the days of wearing 3D glasses with red and blue lenses. Many TV screens, computer monitors, and even cinemas have turned 3D-friendly. To know more about how stereoscopic photography works, you can visit the following links: digital-photography-tips.net/3d-photography.html and wisegeek.com/what-is-3d-photography.htm#.
From Eye to Eye: 3D Photo Maker and Viewer