Leonardo da Vinci described a camera obscura, a darkened room or box that projects an outside scene through a small opening.
Light travels in straight lines through the aperture, forming an inverted image on the opposite surface. Leonardo used the device to investigate vision, light, perspective, and image formation. His notes include detailed observations of how the projected scene behaves inside a dark chamber.
Leonardo did not invent the underlying optical principle; descriptions of camera obscura effects existed in earlier Greek, Chinese, and Islamic scholarship. His contribution was a particularly influential Renaissance treatment of the device and its connection to visual perception and art.
A camera obscura is not a camera with a photographic film or digital sensor. It creates a temporary optical image, which an observer may view or trace. The later development of light-sensitive materials transformed the principle into photography.