Detecting moving objects with background subtraction

To track anything in a video, first, we must identify the regions of a video frame that correspond to moving objects. Many motion detection techniques are based on the simple concept of background subtraction. For example, suppose that we have a stationary camera viewing a scene that is also mostly stationary. In addition to this, suppose that the camera's exposure and the lighting conditions in the scene are stable so that frames do not vary much in terms of brightness. Under these conditions, we can easily capture a reference image that represents the background or, in other words, the stationary components of the scene. Then, any time the camera captures a new frame, we can subtract the frame from the reference image and take the absolute value of this difference in order to obtain a measurement of motion at each pixel location in the frame. If any region of the frame is very different from the reference image, we conclude that...