This is some pretty hefty software. It does everything but tap dance. There is a learning curve, but if you’ve worked before with image manipulation software, you already have a leg up.
I’ve used The Gimp to put text on images for a on-line slide show; to modify the edges of images; to clarify an image; to create a text graphic, and I haven’t begun to test its potential. It’s pretty comprehensive for higher level image work. Although designed on Unix platforms, The Gimp also runs on MS Windows and Mac OS X.
The site is a resource for learning the software, a pretty long list of software features, and there is a very handy users forum, too.