In the photographic process, images are produced by exposing light-sensitive chemicals called silver halides to light. The more light these chemicals are exposed to, the darker they become. After the silver halides are developed and fixed, a negative image is produced. The negative image, which is usually made on film, is then itself exposed to light. The light that passes through it creates a positive image on paper or film containing silver halides. The result of this second exposure is the final photograph.

Some of the theory that makes photography possible has been known since ancient times. The camera obscura, a darkened chamber in which images were projected by letting light enter through a small hole, was known as early as the time of the Greek philosopher Aristotle. In the 17th and 18th centuries, various scientists found that silver nitrate and silver chloride darkened when they were exposed to light. In spite of these findings, however, it was not until 1827 that the first photograph was produced by the French physicist Joseph Niépce. In 1829, Niépce went into partnership with Louis Daguerre, who continued to experiment with photography after Niépce's death and ultimately invented what became known as the daguerreotype process. Daguerre reduced the time required to create an image from eight hours to 30 minutes, and he discovered that the resulting image could be made permanent if it were immersed in salt.

Daguerre's process, although expensive, became extremely popular. People found it exciting that those without drawing or painting skills could create an image by using a chemical process. The new popularity of photography led various people to invent cheaper and more efficient processes. It soon became possible to create multiple copies of a photograph, which was something that the daguerreotype process could not do. In a relatively short period of time, the profession of photography became commercially viable, since many people wanted to have portraits and other photographs made.

Motion-picture photography was invented in 1890 by Thomas Edison, who constructed a kind of camera that would expose the roll film that was first marketed in 1889 by George Eastman, the inventor of flexible film and the Kodak box camera. Other inventions in this new art form soon followed, including the Cinematographe, a portable motion-picture camera that included a film-processing unit and projector. By the early 1900s, motion pictures were being projected to a wide audience who paid for the entertainment.

Although photography became popular soon after its invention, it was not viewed as an art form until much later, after a succession of great photographers had demonstrated the photographic medium to be flexible, immediate, and expressive. Many early critics of photography believed that it was, by its very nature, shallow and narcissistic, and some critics even viewed photography as satanic.

One of the many photographers who contributed to the development of photography as an art form was Mathew Brady, who, along with other photographers, documented the American Civil War. He created works of tremendous power, recording the horrors of war in a way that had not been done before. Some of the many important photographers of the 20th century were art photographers, such as the Americans Ansel Adams, Edward Steichen, Edward Weston, and Alfred Stieglitz, and the French avant-garde artist Man Ray. The field of photojournalism was pioneered by such important figures as Henri Cartier-Bresson, Margaret Bourke-White, and Alfred Eisenstadt.

Cameras and photo processing have changed dramatically since the advent of computer technology. Most cameras manufactured today are battery-operated and allow nearly foolproof picture taking by automatically setting shutter speed, lens aperture, and focus. One of the most important developments is digital photography. In the 1980s, Kodak scientists invented the first megapixel sensor and introduced digital photography products. The first digital cameras for consumers were on the market in the mid-1990s,

In digital photography, instead of using film, pictures are recorded on microchips, which can then be downloaded onto a computer's hard drive. They can be manipulated in size, color, and shape, eliminating the need for a darkroom. Digital photography is now everywhere, and professionals and amateurs alike can create and share images on their Web sites and through Facebook, YouTube, and other social media sites.

The growth of smartphones that feature increasingly powerful digital cameras has enabled more people than ever before to take pictures and videos and process them using apps. This proliferation has also blurred the lines between professional and amateur photographers. To stay relevant in the field, professionals must continually hone their technical skills and keep aware of technological developments in the industry.