"Hand-colouring (or hand-coloring) refers to any method of manually adding colour to a black-and-white photograph, generally either to heighten the realism of the photograph or for artistic purposes.[1] Hand-colouring is also known as hand painting or overpainting.
Typically, watercolours, oils, crayons or pastels, and other paints or dyes are applied to the image surface using brushes, fingers, cotton swabs or airbrushes. Hand-coloured photographs were most popular in the mid- to late-19th century before the invention of colour photography and some firms specialized in producing hand-coloured photographs."