A system of monitoring movable articles, e.g. for detecting counterfeits, is described. It comprises applying to the article (30) a label thereon, coded data in the form of a visually perceptible marking (34) conveniently at the time and place of manufacture and using a digitally controlled printer. Details of the marking are stored in a high capacity memory store. When it is desired to monitor the article, a pictorial image of the marking is sent from the location of the article to a remote computer (37) via a wide area communications network, such as a mobile telephone network (50). Details concerning the location of the article are also transmitted to the remote computer, which is programmed, to extract the coded data from the transmitted image file, and evaluate whether the coded data matches coded data stored in the high capacity memory store. If there is a match, the item is genuine and the remote computer can return a message to that effect.