It is the rectangular area within which the image is composed by the photographer.

The setting for the image is the picture frame. In photography, the format of this frame is fixed at the time of shooting, although it is always possible later to adjust the shape of the frame to the picture you have taken.

Depending on the subject and on the treatment the photographer chooses, the edges of the frame can have a strong or weak influence on the image. For example horizontal and vertical borders, or even the corners, contribute strongly to the design of the photographs. They can be used as references for diagonal lines within the pictures or to interact strongly with the lines of the image.

Most photography is composed to a few rigidly defined format frames (aspect ratios), unlike in other graphic arts. Until digital photography, by far the most common format was 3:2—that of the standard 35mm camera, measuring 36x24mm—but now that the physical width of film is no longer a constraint, the majority of low- and middle-end cameras have adopted the less elongated, more “natural” 4:3 format that fits more comfortably on printing papers and monitor displays.