'A camera lucida is an optical device used as a drawing aid by artists.' - Wikipedia The basic concept is to overlay two separate images into a single image that the artist can see. In the original device the two images were combined with a prism, allowing the artist to see the subject in front of them combined with their sketch pad below them. This allowed them to make an accurate tracing of the subject. In this App there are four modes that allow you to combine live images from webcams, still images from photgraphs and on-screen drawing.