Most photographs are created using a camera , which uses a lens to focus the scene's visible wavelengths of light into a reproduction of what the human eye would see. The process and practice of creating such images is called photography. He exposed a silver-plated copper sheet to iodine vapor, creating a layer of light-sensitive silver iodide ; exposed it in the camera for a few minutes; developed the resulting invisible latent image to visibility with mercury fumes; then bathed the plate in a hot salt solution to remove the remaining silver iodide, making the results light-fast. He named this first practical process for making photographs with a camera the daguerreotype , after himself. Its existence was announced to the world on 7 January but working details were not made public until 19 August.