A
latent image is an invisible image produced by the exposure to
light of a photosensitive material such as
photographic film. When photographic film is
developed, the area that was exposed darkens and forms a visible image. In the early days of photography, the nature of the invisible change in the
silver halide crystals of the film's
emulsion coating was unknown, so the image was said to be "latent" until the film was treated with
photographic developer.