If we take a series of images in time, and there are moving objects in the scene, or perhaps the camera is itself on some moving vehicle, useful information about what the image contains can be obtained by analysing and understanding the difference between images caused by the motion.
For example, given an image of a moving car, deciding which pixels in the image represent motion can help to decide which pixels belong to the car, and which to the static background.
Studying the motion in detail, we can answer such questions as
From an image sequence, we calculate a new function called the optical flow. For every pixel,