Motion blur

When an image of moving objects or from a moving camera is created it does not always merely represent a single instant of time. Often because of technological constraints or artistic requirements the image must represent the scene over a period of time. As objects move in a scene over time an image of that scene must represent an integration of all positions of a camera's viewpoint and object positions over the period of exposure determined by the shutter speed. Any moving object with respect to the camera in such an image will look blurred or smeared along the direction of relative motion, this smearing may occur on an object that is moving or on a static background if the camera is moving.

Because the effect is caused by the relative motion of the camera, object and scene being imaged, the camera may be used to track moving objects by panning the camera such that even with long exposure times motion blur is avoided on the moving object but instead appears on the background.