Short bio: Computer Scientist, FOSS supporter (read more)
Tux Machines (TM)-specific
The Linux world is filled with numerous capable packages for just about every computing category. Graphics manipulation applications are no exception. In any list of able-bodied graphics candidates, GIMP 2.6 should be one of the top three contenders.
GIMP is Linux Speak for GNU Image Manipulation Program. It is a free powerhouse that sets the standard for displaying and tweaking all things photographic on a computer screen. It is a very close first cousin to the not-so-open-source program known as Adobe's Photoshop.
In the high-end category of graphic manipulation apps, GIMP is one of a few high-caliber players. Programs in this high-performance class are not photo cataloging viewers the likes of Google's Picasa. They are advanced photo manipulation and retouching tools.
GIMP became my de facto benchmark measurement for similar photoshopping apps. The fact that GIMP runs on both of my Linux workhorse distros -- Ubuntu and Puppy Linux -- made using it a real bargain.