Daguerreotype...

The daguerreotype is an early type of photograph, developed by Louis Daguerre. It is where an image is exposed directly onto a mirror-polished surface of silver plate which has a coating of silver halide particles on it which are light sensitive; these are deposited by iodine vapour. In later developments bromine and chlorine vapours were also used, resulting in shorter exposure times. The daguerreotype is a negative image, but the mirrored surface of the metal plate reflects the image and makes it appear positive in proper light. This makes the daguerreotype a direct photographic process without the capacity for duplication. The invention was announced to the public on August 19, 1839 and was one of the first types to capture a “true likeness” of an individual. Popularity of the daguerreotype declined in the late 1850s when the ambrotype, a faster and less expensive photographic process, became available.

Info from my knowledge after reading up after Picture Paradise and www.daguerre.org/dagfaq.php

The following image was borrowed from Photomuse @ www.photomuse.org