GNU Image Manipulation Program (GIMP)
A freely distributed program for tasks like photo retouching, image composition and image authoring.
When you think Open Source software, you may think of half-baked programs too hard to use, or perhaps lacking power. Well, think again. This Open Source image editor packs a surprising amount of power, and is well-designed, if a bit eccentric in layout. Even though it’s free, it compares favourably to the power of Photoshop, and includes many of the kinds of photo-editing tools that come with that program, including filters, effects, masks, layers, and more.
Of course there are the basics tools you’d expect in a photo editor, such as red eye removal, but there is plenty more here. If you’re looking for professional-level photo editing, but don’t want to spend a bundle — or even a penny — this is the program for you.
Note: This link takes you to the vendor’s site, where you can download the version of the software appropriate to your system.
Note from developers: GIMP releases available from gimp.org and its mirrors contain the source code and have to be compiled in order to be installed on your system.