A camera obscura usually uses a convex lens or a sheet with a hole in it to project an image onto a surface.

First mention of a camera obscura was by a Chinese philosopher Mo Ti in fifth century BC. Aristotle, Alhazen of Basra, Leonardo Da Vinci, Reinerus Gemma-Frisius, and Johannes Kepler all studied camera obscura, mostly for the purpose of observing solar eclipses. Camera obscura was first thought to be used for artistic purposes by a Dutch painter Jan Vermeer in the 17th century.

Jan Vermeer used a home made camera obscura, to project an image, he placed the objects and/or people in the light. Then he acquired a canvas and placed it, so that it would be facing the subjects. Next he placed a lens or a sheet with a hole in it between the subjects and the canvas. Then he focused the image on the canvas by adjusting the distance between the lens, the object, and the canvas. Lastly he outlined or painted over the image on the canvas.

This technique creates art work with extremely correct perspective. The color shades and hues can be matched very accurately as well. One down fall of this technique is that if the subject has significant depth, camera obscura can only be focused on one part of it. Thus objects that are close up, and far away appear blurry.

Please note, it is still hotly debated if Vermeer used camera obscura. However the method would still remain the same.