This photo was created using a primitive single-lens camera and silver chemistry, techniques that date back to the 1850s and the early years of photography.
Lewis Dartell, author of The Knowledge: How to Rebuild Our World from Scratch describes the process in his book-
"The crucial chemistry behind photography is simple enough: certain compounds of silver darken in sunlight and so can be employed to record a black-and-white image. The trick is to create a soluble form of silver that can be spread evenly in a thin film, but then convert it into an insoluble salt that sticks on the outside surface of your photographic medium and doesn’t get washed away again.
First, coat a sheet of paper with egg whites containing some dissolved salt, and allow it to dry. Now dissolve some silver in nitric acid, which will oxidize the metal to soluble silver nitrate, and spread the solution over your prepared paper. The sodium chloride will react to create silver chloride, which is both light-sensitive and insoluble, and the egg albumin will prevent the photographic emulsion from soaking into the paper fibers. If you scavenge in the post-apocalyptic world, a single solid-silver teaspoon will contain enough of the pure element to produce over 1,500 photographic prints.
When light rays hit this sensitized paper, they provide the energy to liberate electrons in the grains and so reduce the silver chloride back to metallic silver. Large lumps of silver, such as a polished platter, have a bright luster, but a speckle of tiny metallic crystals scatters the light instead and so looks dark. On the other hand, areas of the sensitized sheet not exposed to light remain the white of the paper behind. The key follow-up step after the exposure is to kill this photochemical reaction and so stabilize the captured shadows. Sodium thiosulfate is the fixing agent still used today and is relatively easy to prepare. Bubble sulfur gas through a solution of soda or caustic soda, then boil with powdered sulfur and dry for crystals of “hypo” (a nickname derived from its old name, hyposulfite of soda).
Using a lens set into the front of a light-tight box to project an image onto sensitive paper on the back wall produces a photographic camera, but even in bright sunshine it can take many hours for this rudimentary silver chemistry to take a “photo.” Luckily, you can increase the sensitivity of your camera enormously with a developer—a chemical treatment that completes the transformation of partially exposed grains, reducing them entirely to metallic silver. Ferrous sulfate works well, and can be synthesized easily enough by dissolving iron in sulfuric acid. And as the chemical proficiency of the post-apocalyptic society improves, in place of chlorine salt you can substitute that of one of its atomic siblings, iodine or bromine, which produce far more light-sensitive photographic emulsions.”
Read the rest of the excerpt here