The word photography is derived from the greek words for light and writing. Sir John Herschel, was the first to use the term "Photography". This was in 1839, the year the photographic process became public. There are two distinct scientific processes that combine to make photography possible. These processes had been known for quite some time, so it is somewhat surprising that photography was not invented earlier than the 1830s. It was not until the two distinct scientific processes had been put together that photography came into being.
The first of these processes was optical. The Camera Obscura (dark room) had been in existence for at least four hundred years. The second process was chemical. For hundreds of years before photography was invented, people had been aware, for example, that some colors are bleached in the sun, but they had made little distinction between how heat, air, and light created reactions.
In the sixteen hundreds Robert Boyle, a founder of the Royal Society, had reported that silver chloride turned dark under exposure. He believe that it was caused by exposure to the air, rather than to light.
Angelo Sala, in the early seventeenth century, noticed that the sun blackened powdered nitrate of silver. In 1727 Johann Heinrich Schulze discovered that when exposed to light, certain liquids change color. At the beginning of the nineteenth century Thomas Wedgwood was conducting experiments with pictures. He had successfully captured images, but his silhouettes wouldn't stay, as there was no known method of making the image permanent.
Niépce successfully produced a picture in July of 1827. He used a material that hardened on exposure to light. The down side is that the picture required an 8 hour exposure. Niépce agreed to go into partnership with Lousi Daguerre on January 4, 1829. Although Niépce died 4 years later, Daguerre continued to experiment. Daguerre discovered a way of developing photographic plates. This process would greatly reduce the amount of exposure time. Instead of 8 hours it would only take half an hour. Daguerre also discovered that by dipping it in salt the image could be made permanent. The Daguerreotype was bought by the French Government and made public on Aug. 19, 1839.
William Henry Talbot had an invention called the Calotype. The Calotype produced a negative picture on paper. That means the lights were recorded as darks, and the darks as lights. The positive was made on another sheet of chemically sensitized paper, exposed to light through the negative. An infinite number of positives could be made from a single negative so Talbot's invention and refinements of it predominated.
Photographers were like artists because they recorded contemporary events only with greater flexibility and on a much greater scale. One of the first photographic documents of history-in-the-making was also the greatest. This was the American Civil War. These were made by 20 photographers. Most of them were initially under the direction of Mathew B. Brady. They could not yet capture the action of battle with their big equipment, but their blunt views of landscapes, littered with the dead changed the popular vision of war.