An image created by the interaction of visible light with chemicals to create a change which can be preserved semi-permanently. Photo is a contraction of photograph, a word coined from greek roots to mean "drawing with light".

An image created by the interaction of visible light with chemicals to create a change which can be preserved semi-permanently.

From 1822, combinations of light-sensitive chemicals known to react when "exposed" were used to capture images. Significant improvements in both the chemical processes used and the mechanisms used to gather the light (a camera) enabled the rapid spread throughout the western world of the capacity to produce true-to-life images.

It is possible that ancestors from the 1860s onward might have had photographic portraits made in a studio. When preserved they can provide valuable evidence into aspects of their lives.

Further technological development enabled the taking of photographs to become a personal activity (rather than a professional service) from the 1930s. This means that the number of photographs available is much larger but that (in most cases) their provenance is less clear.

Since the 1980s, images have been captured through the electrical effects of light on semi-conducting materials to produce digital information (rather than on chemical film). Such digital images are now widely available and also called "photos".