GIMP

The GIMP (GNU Image Manipulation Program) is a freely distributed program for such tasks as photo retouching, image composition and image authoring. It has many capabilities. It can be used as a simple paint program, an expert quality photo retouching program, an online batch processing system, a mass production image render-er, an image format converter, etc. GIMP is expandable and extensible. It is designed to be augmented with plug-ins and extensions to do just about anything.