Artists who dabble in realistic imagery use vanishing points to enhance the believably of the scene. Vanishing points give the illusion of a three-dimensional scene by making objects appear farther away from the viewer by making them smaller. Finding vanishing points is easiest in landscapes, but cityscapes, portraits and even general photographs use this technique.
Find a line or object in the piece that is horizontal and level within the context of the picture. Objects such as these can include railings, boxes, roads or buildings.
Cover the picture with a piece of tracing paper. Flatten the paper so that you can see the scene through the fibers.
Trace the horizontal object onto the tracing paper. Also trace any lines or objects that are parallel to it. These lines should all appear to converge somewhere in the distance.
Move the tracing paper from the picture to a larger sheet of paper. Extend the traced lines straight beyond the boundaries of the trace paper onto the large paper. Use a ruler to extend the lines until they meet. Where they meet is the vanishing point of the piece.
Move the tracing paper and put the actual picture on top of the large paper. Now the lines of the horizontal objects in the picture should appear to extend onto the large paper. Make a mental note of where the vanishing point is in relation to the picture. Note how sometimes it is not actually in the piece itself.
Repeat this process with picture that you are able to remove from frames and trace. With practice you will be able to discern the vanishing points without the need to trace.