The Science Behind Facebook’s 3D Photos –TechCrunch

The phone’s two cameras take a pair of images, and immediately the device does its own work to calculate a “depth map” from them, an image encoding the calculated distance of everything in the frame […] [T]he user takes multiple images of their surroundings by moving their phone around; it captures an image (technically two images and a resulting depth map) every second and starts adding it to its collection. In the background, an algorithm looks at both the depth maps and the tiny movements of the camera captured by the phone’s motion detection systems.

If you’re interested in the technical details of the technology, you can give the paper a read.