The article develops an analysis of visual knowledge and the use of pictures in electronic communication. The author focuses in particular on indexical images, which we use in navigat-ing multimedia documents and the Web. For this purpose, the author bases his study on the one hand on semiotics, the core concepts of which were intro-duced by C.S. Peirce at the beginning of the last century; and on the other hand on a more classical historical analy-sis, in order to point out the deep roots of the concepts used in contemporary computer-based communication.