GIMP Image Editor

The GIMP is a free, open source raster image editor.

You can use it in similar ways to Adobe’s Photoshop.  I use it at least once a day to touch up photos or to create images for advertisements for clients.

It has a quirky interface when compared with Photoshop, but really, Photoshop has a quirky interface, too (There’s nothing intuitive about editing images)!

http://www.gimp.org/release-notes/gimp-2.6.html