Gimp and Kpaint cover the extreems of image manipulation porgrams. Kpaint is very simple while GIMP is very rich. There are programs in between and many specialty drawing tools, such as CD lable programs, that will not be covered here. I just did not have the time to include them.
GIMP 1.2 and GIMP 2 are covered because both have their place. Gimp takes less screen space and is beter suited to older hardware. GIMP can be run on a 75MHz PI with a 640x480 screen. Zooming and other manipulations are fast. GIMP2 has many excellent improvements and should be used where hardware is not an issue.
Image Magic provides back end libraries for everyone and can be used for batch processing and automated image manipulation. See the references for more information.