The GIMP is an image manipulation program suitable for photo retouching,
image composition and image authoring. Many people find it extremely
useful in creating logos and other graphics for web pages. The GIMP has
many of the tools and filters you would expect to find in similar
commercial offerings, and some interesting extras as well.
The GIMP provides a large image manipulation toolbox, including channel
operations and layers, effects, sub-pixel imaging and anti-aliasing, and
conversions, all with multi-level undo.