An old photograph is a daguerreotype, which is a photographic process developed in the early 19th century by Louis Daguerre. It was the first publicly available photographic process and involved exposing a silver-plated copper sheet to iodine vapor, creating a coating of light-sensitive silver iodide. The exposed plate was then exposed in a camera and developed in mercury vapor. The resulting image was a one-of-a-kind direct positive that could not be reproduced.