These generally fall into one of two categories. They are bitmap or vector graphics. A picture can be stored as a simple copy of the original. This is a collection of very small rectangles, rather like making a picture by colouring individual squares on graph paper, called a bitmap image. If it is enlarged, the small rectangles are simply made bigger and the image loses its sharpness.
Some computer programmes save pictures as vector images.
In this case the picture is stored as a series of instructions so that every time the picture is enlarged it is effectively redrawn. Vector images can be enlarged without any loss of detail. High capacity disks, which can hold much more information, are available but they require special disk drives to be used. These are widely used on the Internet and CD-ROMs to simplify the selection of further information. Icon A small picture which represents an action or object.