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".
Henry Collen
Calotype was an early photographic process developed by Henry Fox Talbot who was a colleague of Collen's. Talbot supplied the photographic knowledge and Collen the artistic know-how. In an article titled "Photography in the 1840s," Peter Marshall describes the distinction between daguerreotypes and calotypes. "The daguerrotype spread rapidly around the world...There were some limitations on the spread." Daguerre's process was somewhat limited by his prior patent in the UK, and so only those professionals who could afford a license were able to do so. Meanwhile, Talbot patented his calotype process in the UK and the US, but he was unable to get a patent in France which also limited its growth. Also, Marshall states, "In general, most professional photographers used the daguerreotype process in the 1840s, while the calotype was generally favored by those who were not attempting to earn an income." (A chart describing the differences between calotypes and daguerreotypes is included in the Appendix).