A photograph (also known as a photo) is an image created by light falling on a photosensitivity surface, usually photographic film or an electronic image sensor, such as a CCD or a CMOS chip. Most photographs are created using a camera, which uses a lens to focus the scene's visible spectrum of light into a reproduction of what the human eye would see. The process and practice of creating such images is called photography. The word photograph was coined in 1839 by Sir John Herschel and is based on the Greek language φῶς ( phos), meaning "light", and γραφή ( graphê), meaning "drawing, writing", together meaning "drawing with light". Many jurisdictions have laws prohibiting certain types of photographs which may include photos of government buildings, copyrighted content, private property, and child pornography.
After Niépce's death in 1833, Daguerre concentrated on silver halide-based alternatives. He exposed a silver-plated copper sheet to iodine vapor, creating a layer of light-sensitive silver iodide; exposed it in the camera for a few minutes; developed the resulting invisible latent image to visibility with mercury fumes; then bathed the plate in a hot salt solution to remove the remaining silver iodide, making the results light-fast. He named this first practical process for making photographs with a camera the daguerreotype, after himself. Its existence was announced to the world on 7 January 1839 but working details were not made public until 19 August. Other inventors soon made improvements which reduced the required exposure time from a few minutes to a few seconds, making portrait photography truly practical and widely popular.
The daguerreotype had shortcomings, notably the fragility of the mirror-like image surface and the particular viewing conditions required to see the image properly. Each was a unique opaque positive that could only be duplicated by copying it with a camera. Inventors set about working out improved processes that would be more practical. By the end of the 1850s the daguerreotype had been replaced by the less expensive and more easily viewed ambrotype and tintype, which made use of the recently introduced collodion process. Glass plate collodion negatives used to make prints on Albumen print soon became the preferred photographic method and held that position for many years, even after the introduction of the more convenient gelatin process in 1871. Refinements of the gelatin process have remained the primary black-and-white photographic process to this day, differing primarily in the sensitivity of the emulsion and the support material used, which was originally glass, then a variety of film base, along with various types of paper for the final prints.
Color photography is almost as old as black-and-white, with early experiments including John Herschel's Anthotype prints in 1842, the pioneering work of Louis Ducos du Hauron in the 1860s, and the Lippmann plate unveiled in 1891, but for many years color photography remained little more than a laboratory curiosity. It first became a widespread commercial reality with the introduction of Autochrome plates in 1907, but the plates were very expensive and not suitable for casual snapshot-taking with hand-held cameras. The mid-1930s saw the introduction of Kodachrome and Agfacolor, the first easy-to-use color films of the modern multi-layer chromogenic type. These early processes produced transparencies for use in and viewing devices, but color prints became increasingly popular after the introduction of chromogenic color print paper in the 1940s. The needs of the motion picture industry generated a number of special processes and systems, perhaps the best-known being the now-obsolete three-strip Technicolor process.
The production of certain types of photograph has been forbidden under modern laws, such as those of highly classified regions,Masco, Joseph. "“Sensitive but Unclassified”: Secrecy and the Counterterrorist State." Public Culture 22.3 (2010): 433-463. copyrighted worksTurnbull, Bruce H. "Important legal developments regarding protection of copyrighted content against unauthorized copying." IEEE Communications Magazine 39.8 (2001): 92-100. and children's genitalia.Slane, Andrea. "From scanning to sexting: The scope of protection of dignity-based privacy in Canadian child pornography law." Osgoode Hall Law Journal 48 (2010): 543. These laws vary greatly between jurisdictions.
Alternatively, the film is processed to invert the negative image, yielding positive transparencies. Such positive images are usually mounted in frames, called slides. Before recent advances in digital photography, transparencies were widely used by professionals because of their sharpness and accuracy of color rendition. Most photographs published in magazines were taken on color transparency film.
Originally, all photographs were monochromatic or hand-painted in color. Although methods for developing color photos were available as early as 1861, they did not become widely available until the 1940s or 1950s, and even so, until the 1960s most photographs were taken in black and white. Since then, color photography has dominated popular photography, although black and white is still used, being easier to develop than color.
Panoramic format images can be taken with cameras like the Hasselblad Xpan on standard film. Since the 1990s, panoramic photos have been available on the Advanced Photo System (APS) film. APS was developed by several of the major film manufacturers to provide a film with different formats and computerized options available, though APS panoramas were created using a mask in panorama-capable cameras, far less desirable than a true panoramic camera, which achieves its effect through a wider film format. APS has become less popular and has been discontinued.
The advent of the microcomputer and digital photography has led to the rise of Digital printing. These prints are created from stored graphic formats such as JPEG, TIFF, and RAW. The types of printers used include , dye-sublimation printer, , and . Inkjet prints are sometimes given the coined name "Giclée".
The Web has been a popular medium for storing and sharing photos ever since the first photograph was published on the web by Tim Berners-Lee in 1992 (an image of the CERN house band Les Horribles Cernettes). Today popular sites such as Flickr, Picasa, PhotoBucket and 500px are used by millions of people to share their pictures.