Daguerreotype
It is said that Daguerre has found the means to collect, on a plate prepared by him, the image produced by the camera obscura, in such a way that a portrait, a landscape, or any view, projected upon this plate by the ordinary camera obscura, leaves an imprint in light and shade there, and thus presents the most perfect of all drawings ... a preparation put over this image preserves it for an indefinite time ... the physical sciences have perhaps never presented a marvel comparable to this one.
A further clue to fixing the date of invention of the process is that when the Paris correspondent of the London periodical "The Athenaeum" reported the public announcement of the daguerreotype in 1839, he mentioned that the daguerreotypes now being produced were of considerably better quality than the ones he had seen "four years earlier".
Daguerreotype
Conservators were able to determine that a daguerreotype of Walt Whitman was made in New Orleans with the main clue being the type of frame, which was made for wall hanging in the French and continental style. Supporting evidence of the New Orleans origin was a scrap of paper from "Le Mesager", a New Orleans bilingual newspaper of the time, which had been used to glue the plate into the frame. Other clues used by historians to identify daguerreotypes are hallmarks in the silver plate and the distinctive patterns left by different photographers when polishing the plate with a leather buff, which leaves extremely fine parallel lines discernible on the surface.