Photography is a technique, including processes and materials, that consists in fixing or reproducing over time accurate images of the real world on a photosensitive medium (silver photosensitive chemical with film or paper, digital sensor) by exposure to visible or non-visible light, such as infrared.

Initially developed for the cinema, the 35mm film format was later adopted by silver photography under the name "small format", in a practical package, the 135 cartridge containing the photosensitive film. In photography, the image size is 24 x 36 mm. For various reasons (including the use of optics developed for 24x36), digital photography has retained this format for the sensors of high-end SLR cameras.