Article: Double-Exposure Photography - N. Dombrowski ; A. Levy Nature (1964)

• The velocity of a moving object may be determined by taking two photographs of it on the same photographic emulsion separated by a known interval of time and measuring the distance through which the image has moved.
• Double exposure of non-luminous objects can be carried out with transmitted light where the camera lens is presented with a silhouette of the object against a light background, or with some other type of lighting such as frontal illumination, where the object appears bright against a dark background.