Most of us think (at least I used to think) that creating 3D photographs is a new thing and technologies involved are recent. When I visit Camera Museo in Gurgaon, Aditya Arya showed an equipment to view 2D Photograph and you start seeing the depth, which you get in 3D. And this equipment was at least 100 years old. This was interesting and that made me think about the physics behind 3D. So the photograph placed on this equipment is not a normal 2D photograph, but a photograph which has 2 photographs side-by-side (check out 150 years old 3D photographs here). So it simulates the view seen by our eyes. The next obvious question comes that how a photograph would click these two photographs of same view and ensure that view-point is changed by appropriate distance.
There are 3D cameras which used to click these side-by-side 2D photographs. There was time when these cameras were extremely popular. Lot of World War 2 photographs are clicked with such cameras. I am still finding it hard to explain this 150 years old technology in this post but experts like Aditya Arya can share these details more appropriately. If you are interested in knowing/understanding these amazing old technologies in photography world, it makes sense to plan a visit to Museo Camera in Gurgaon.