Traditional 3D Methods (Passive)
There are many ways to create an image that will fool your brain into thinking a 2 dimensional surface has 3 dimensions. Years ago, all we had were Red/Blue blocking 3D glasses a lá Match from Back to the Future. This technology involves filming in stereo where the camera has 2 lenses spaced apart to record video just like how your eyes see. It’s kind of like looking through a periscope on a submarine but instead of bouncing the light down the tube with mirrors, it is bounced through time on film. Your left eye should only see what was recorded by the left lens and your right eye should only see what was recorded by the right lens. Your brain then uses all kinds of fancy geometry to assemble these two images back into one 3D view of the world
Similar technology is used these days with digital projection where you have polarized lenses where each lens is designed to block/permit light that is polarized in a certain way. Whatever the left lens blocks is permitted to go through the right lens and vice versa. The easiest way to demo this is if you have a pair of leftover glasses from your last movie theater 3D outing, put them on, look at yourself in a mirror, and close one eye. You won’t be able to see your other eye behind the glasses in the reflection because the light that passes through the glasses has been fully blocked, neat huh? When you are in the movie theater, the projector swaps between polarization for the left and right eye something like 120 times a second (as opposed to a normal projector which only needs to flash frames at 29.97 frames per second to prevent flickering as detected by the human eye/brain).
Older polarizing 3D attractions at places like Disneyland use a similar technique, but I have a feeling they use two separate projectors rather than just switching back and forth on one projector. That’s why sometimes when one projector isn’t as bright as the other you get this really wonky effect where it feels like you can’t see through one eye and you think the glasses are dirty.
3D Stereo Photography via “Jiggle Effect”
Another way to do it is by switching back and forth between two static images taken slightly apart from one another. You can see a bunch of cool examples of this method here. When I was going through the pictures from my recent Disneyland trip, I came across a couple pictures in a row that seemed by a jolly accident to work with this effect.
If you click to embiggen the image, the effect is easier to see.