Daguerreotype (/dəˈɡɛr(i)ətp, -r(i)-/; English pronunciation;[1][2][3] French: daguerréotype) was the first publicly available photographic process; it was widely used during the 1840s and 1850s. "Daguerreotype" also refers to an image created through this process.

Daguerreotype of Louis Daguerre in 1844 by Jean-Baptiste Sabatier-Blot

Invented by Louis Daguerre and introduced worldwide in 1839,[4][5][6] the daguerreotype was almost completely superseded by 1860 with new, less expensive processes, such as Ambrotype, that yield more readily viewable images. There was a revival of daguerreotype in the late 20th century by a small number of photographers interested in making artistic use of early photographic processes.[citation needed]

The first authenticated image of Abraham Lincoln, a daguerreotype of him as U.S. Congressman-elect in 1846, attributed to Nicholas H. Shepard.

To make the image, a daguerreotypist polished a sheet of silver-plated copper to a mirror finish; treated it with fumes that made its surface light sensitive; exposed it in a camera for as long as was judged to be necessary, which could be as little as a few seconds for brightly sunlit subjects or much longer with less intense lighting; made the resulting latent image on it visible by fuming it with mercury vapor; removed its sensitivity to light by liquid chemical treatment; rinsed and dried it; and then sealed the easily marred result behind glass in a protective enclosure.

The image is on a mirror-like silver surface and will appear either positive or negative, depending on the angle at which it is viewed, how it is lit and whether a light or dark background is being reflected in the metal. The darkest areas of the image are simply bare silver; lighter areas have a microscopically fine light-scattering texture. The surface is very delicate, and even the lightest wiping can permanently scuff it. Some tarnish around the edges is normal.

Several types of antique photographs, most often ambrotypes and tintypes, but sometimes even old prints on paper, are commonly misidentified as daguerreotypes, especially if they are in the small, ornamented cases in which daguerreotypes made in the US and the UK were usually housed. The name "daguerreotype" correctly refers only to one very specific image type and medium, the product of a process that was in wide use only from the early 1840s to the late 1850s.