What discovery was the basis of photography?

The camera is often thought to be a modern invention. But as early as 1727, a German physicist discovered that light darkened silver salt, a chemical compound. Using as a camera, a big box with a small hole to let the light in, he made temporary images on the salt. Silver salt is still the base of film today. Then a French scientist made the first permanent picture by using a special piece of metal sensitized with silver salt. A photography he made in 1826 still exists. The painter Dagear improved on the process by placing common salt, the kind we eat, on the metal. This was in 1839, the official date of the beginning of photography. But the problem was the printing of the photographs. And it wasn’t until other scientists developed the kind of paper we now use that good printing was possible and photography became truly modern. In 1860’s Matthew Brady was able to take his famous pictures of the American Civil War, thus making portrait poses very popular.