Typically photo-finish cameras use strip photography, in which a camera is aimed at the finish line from an elevated position in a tower. It captures only the sequence of events on that line in the vertical dimension. Every part of each racer's body is shown as it appeared the moment it crossed the line; anything stationary is represented as a horizontal streak. The horizontal position represents time, and time markings along the bottom of the photo can be used to find the exact crossing time of any racer. The high angle allows judges to see the position of every racer in relation to the others.
Historically, motion picture cameras had been used in the United States since the 1920s for recording race-meets but were unsuitable for photo-finish photography as the frame rate was too infrequent to catch the critical instant when horses or dogs reached the finish line. This was achieved by using a special slit camera. Lorenzo Del Riccio, a Paramount Pictures motion picture engineer improved the circular flow camera, a device which had been invented in the 1930s especially for the purpose of photographing moving objects. The first racing club to make use of Del Riccio's 'Photo-Chart' camera for photo finishes was the Del Mar Turf Club in California at its inaugural meeting in 1937. 2b1af7f3a8