Illustrations used from an already available source, usually a commercial vendor of images. The first stock art was called "clip art" and generally consisted of low resolution black and white paintings. The next generation was variable resolution vector art, usually in
EPS format, such as that created by PostScript illustration programs like Freehand. Today, all those still exist, but the most popular format is high resolution TIFF images, either royalty-free photography or original illustrations. They are generally available as low resolution FPO images, or "comps", and high resolution versions which must be purchased.