Hanover College
Hanover College: Use of Visual Information in Art
This site from Hanover College gives a tutorial on issues of visual representation, such as depth, perspective, texture, shadow, illusion. Begins at an introductory level. Numerous pictures.
J. Paul Getty Trust
J. Paul Getty Museum: Drawings by Rembrandt and His Pupils
Compare and contrast drawings by Rembrandt with those of his students to learn about his characteristic visual traits, especially his approach to line and his use of light and shadow to create the illusion of three dimensions.