DX (Digital indeX) encoding is a standard for marking 35 mm and APS photographic film and film cartridges, originally introduced by Kodak in 1983. It includes multiple markings, which are a latent image barcode on the bottom edge of the film, below the sprocket holes, a conductive pattern on the cartridge used by automatic cameras, and a barcode on the cartridge read by photo-finishing machines.
The DX encoding system was incorporated into ANSI PH1.14, which provided standards for 135 film magazines for still picture cameras and was superseded by NAPM IT1.14 in 1994; it is now part of ISO standard 1007, whose latest revision was issued in 2000.