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".
Photoengraving
The use of photoengraving for a halftone process that could be used to print grayscale photographic images dates all the way back to the 1839 introduction of the daguerreotype, the first practical photographic process. The daguerreotype image consisted of a microscopically fine granular structure on the surface of a silver-plated copper sheet that had been polished to a mirror finish. Methods were soon devised for differentially etching the image grains and the ground so that the daguerreotype could be used as a printing plate. In some instances, very pleasing results were obtained, but exceptional skill and care were required and the very fine structure of the image limited the useful life of each plate to a few hundred prints at best.