ImageJ: Image Processing and Analysis in Java.

IrfanView is a freeware (for non-commercial use) graphic viewer for Windows 9x/ME/NT/2000/XP/2003.

ITK allows to process images in a number of different ways, through the use of its filtering objects.

Camera RAW workflow software enabling digital photographes to efficiently download, browse, view, prioritize, compare, edit, correct and convert large batches of digital camera RAW image files.

GIMP is the GNU Image Manipulation Program, a freely distributed piece of software for such tasks as photo retouching, image composition and image authoring.

XnView is an utility for viewing and converting graphic files.