From the Greek photos = light, and graphis = stylus, paintbrush or graphê = representation by means of lines, drawing. Photography literally means "drawing with light".
Photography is the technique of recording, by chemical or mechanical means, a permanent image on a layer of material sensitive to light exposure. The understanding that prevails today assumes the use of a camera or camera obscura as the image forming device, and of photographic film as the recording medium, but it doesn't have to be the case. For instance, the photocopy or xerography machine is forming permanent images from a brightly lit original, but is using the transfer of static electrical charges rather than photographic film, hence the term electrophotography. Whereas the rayographs published by Man Ray in 1922 are images produced by the shadows of objects cast on the photographic paper, without the use of a camera.
Photography can be classified under the wider denomination of imaging technology and, as such, has gained the interest of both scientists and artists from its very beginning. Scientists have been interested by its capacity to make accurate recordings, as Eadweard Muybridge in his study of human and animal locomotion (1887). Artists have been equally interested by this aspect but have also tried to explore other avenues than the photo-mechanical representation of reality, as the pictorialist movement did.
The first photograph is considered to be an image produced in 1826 by Nicéphore Niepce on a polished pewter plate covered with a petroleum derivative called bitumen of Judea. It was produced with a camera, and required an eight hour exposure in bright sunshine ! In 1839 Jacques Daguerre developed a process using silver on a copper plate called the Daguerreotype. It is somehow similar to instant photography as it is the exposed material that is handed over to the user, after processing. Almost at the same time, William Fox Talbot developed a different process called the calotype, using paper sheets covered with silver chloride. This process is much closer to the photographic process in use nowadays, as it produces a negative image that can be reused to produce several positive prints.
At the time, the Daguerreotype proved more popular as it responded to the demand for portraiture emerging from the middle classes in midst of the industrial revolution. In fact, this demand for portraits, that could not be met in volume and in cost by oil painting, may well have been the push for the development of photography. Neither of the techniques involved, the camera obscura, and the photo sensitivity of silver salts, were 19th century discoveries. Camera obscura were used by artists in the 16th century, as an aid to sketches for paintings, and the photo-sensitivity of a silver nitrate solution was observed by Johann Schultze in 1724.
Ultimately, the photographic process came to be a series of refinements and improvements on the foundations laid by William Fox Talbot. Photography became a mass-market opportunity in 1901 with the introduction of the Kodak Brownie camera, and more importantly with the industrialisation of film processing and printing. For the layman using a point-and-shoot camera 100 years later, very little has changed in principle since then. As for the enthusiast photographer processing black and white film, very little has changed since the introduction of the 35mm film Leica camera in 1925.
This situation was to be a considerable burden for photographers on remote locations without access to processing facilities like press correspondants. Under increased pressure from television to deliver their images to the newspapers ever faster, photo-journalists on remote loations, would carry a miniature photo lab with them, and some means of transmitting their images down the telephone line. In 1990, Kodak unveiled the DCS 100, the first commercially available digital camera. Its cost precluded any other use than photojournalism and professional applications, but commercial digital photography was born.
In 10 years, digital cameras have become consumer products, and they are likely to replace their traditional counterparts as the price of electronic components goes down, whilst the chemical photographic process still depends on the cost of the chemicals and more specifically those of gelatin and silver.