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".
Louis Daguerre
After the death of Niépce in 1833, Daguerre concentrated his attention on the light-sensitive properties of silver salts, which had previously been demonstrated by Johann Heinrich Schultz and others. For the process which was eventually named the daguerreotype, he exposed a thin silver-plated copper sheet to the vapour given off by iodine crystals, producing a coating of light-sensitive silver iodide on the surface. The plate was then exposed in the camera. Initially, this process, too, required a very long exposure to produce a distinct image, but Daguerre made the crucial discovery that an invisibly faint "latent" image created by a much shorter exposure could be chemically "developed" into a visible image. Upon seeing the image, the contents of which are unknown, Daguerre said, "I have seized the light – I have arrested its flight!"