Optical flow is the distribution of the apparent velocities of objects in an image. By estimating optical flow between video frames, you can measure the velocities of objects in the video. In general, moving objects that are closer to the camera will display more apparent motion than distant objects that are moving at the same speed.
Optical flow estimation is used in computer vision to characterize and quantify the motion of objects in a video stream, often for motion-based object detection and tracking systems.
See also: motion estimation, object detection, object tracking, image stabilization, image processing and computer vision, image recognition, object recognition, digital image processing, feature detection, feature matching, feature extraction, ransac, point cloud