Hippolyte Bayard (20 January 1807 – 14 May 1887) was one of the earliest photographers in the history of photography, inventing his own photography process known as direct positive printing and presenting the world’s first public exhibition of photographs on 24 June 1839.

The direct positive process involved exposing silver chloride paper to light, which turned the paper completely black. It was then soaked in potassium iodide before being exposed in a camera. After the exposure, it was washed in a bath of hyposulfite of soda and dried. The resulting image was a unique photograph that could not be reproduced. Due to the paper’s poor light sensitivity, an exposure of approximately twelve minutes was required. Using this method of photography, still subject matter, such as buildings, were favored. When used for photographing people, sitters were told to close their eyes so as to eliminate the eerie, “dead” quality produced due to blinking and moving one’s eyes during such a long exposure. Read full wikipedia article.