Parallel lines in a picture which are not parallel to the visual plane of the picture appear to converge in one or more vanishing points inside or outside the borders of the image. It is useful to analyse a motion still regarding its vanishing points because they can help to determine the height of the camera and the camera angle. If a motion still has only one vanishing point, it is possible to draw a horizontal line across it and get the so-called “horizon line”, which marks the height of the camera at the moment the frame was taken. If there is more than one vanishing point, it is necessary to find two opposite vanishing points, which are mostly located offscreen, and draw a line from one vanishing point to the other to get the horizon line. If a horizon line slopes in one direction, it shows that the camera was canted to one side.
