Photochrom, Fotochrom, Photochrome or the Aäc process is a process for producing colorized images from a single black-and-white photographic negative via the direct photographic transfer of the negative onto lithographic printing plates. The process is a photographic variant of chromolithography. Because no color information was preserved in the photographic process, the photographer would make detailed notes on the colors within the scene and use the notes to hand paint the negative before transferring the image through colored gels onto the printing plates.

Hand-colouring refers to any method of manually adding colour to a monochrome photograph, generally either to heighten the realism of the image or for artistic purposes. Hand-colouring is also known as hand painting or overpainting.