People were experimenting with photosensitivity as early as the 1400's, but it was French artist Louis Daguerre who worked out the kinks in the nineteenth century.
Daguerre and his partner Nicéphore Niépce took the experimentation farther from the silver nitrate and bitumen-based methods already known. Niépce died in 1833, but Daguerre continued to tinker.
An accident involving a mercury thermometer in 1835 led Daguerre to advances in his method and he produced the first image with his process of exposure, development and fixation in 1837.
Daguerre secured a patent for his process in Britain on August 14, 1839. He attempted to secure a patent in France as well, but on August 19, 1839, the French government offered the secrets of the daguerreotype "as a free gift to the world." France did, however, award Daguerre a pension for his discovery.