Leonardo da Vinci described a camera obscura, an optical device that projects an outside scene into a darkened room.
Light enters through a small aperture and forms an inverted image on the opposite wall or screen. In his notebooks, Leonardo compared the effect to the way the eye receives images and used diagrams to analyze rays of light.
The principle was known before Leonardo, with descriptions by ancient Greek and Islamic scholars. His importance lies in detailed observations and practical experiments, including suggestions for using lenses and mirrors to improve the image.
A camera obscura is an ancestor of the photographic camera, but it does not record a permanent picture by itself. That distinguishes it from a camera using film or an electronic sensor.