The following is stolen from a book I saw a while ago:
Early photography owes its origin to the discovery of the daguerreotype.
A plate, made of thin copper or other metal, was covered with a silver preparation. This was placed directly in the camera, and there was no method of transfer, as there is from the ordinary photographic plate, from which innumerable prints may be taken.
It went out of common use with the invention of the photographic plates and paper, and with the discovery of instantaneous photography. The taking of the daguerreotype required long exposure, which was decidedly objectionable and the result was coarse and tame.
After taking, the daguerreotype passed through acid solutions for the development and permanency of the picture.