A camera lucida is an optical device used as a drawing aid by artists. The artists see an optical superimposition of the object that is created on the surface of drawing. As in a photographic double exposure, both the object or scene and the drawing surface can be viewed by the artist. The images are traced or the key points of the scene/object are drawn by the artist. The camera lucida was patented in 1807 by William Hyde Wollaston. In 2001, an English artist named David Hockney put forward a theory that more artists than formerly acknowledged used camera lucidas and other lensed devices. One such artist was Jean-Auguste-Dominique Ingres (French, 1780-1867).