The Gimp is the GNU Image Manipulation Program. The GIMP is an application suitable for such tasks as retouching of photographs, composing and authoring images. Its capabilities as an image manipulation program make it a worthy competitor to other similar programs such as Adobe Photoshop or Corel PhotoPaint. It is available for Linix and Windows.
The Unidentified Flying Raw (UFRaw) is a utility to read and manipulate raw images from digital cameras. It can be used on its own or as a Gimp plug-in.
Luminance HDR is an open source graphical user interface application that aims to provide a workflow for HDR imaging.
With Hugin you can assemble a mosaic of photographs into a complete immersive panorama, stitch any series of overlapping pictures and much more.
AutoPano takes a folder and searches it for image files. By analysing the pictures, it attempts to divide them into panorama sets.
AutoStitch takes a step forward in panoramic image stitching by automatically recognising matching images. This allows entire panoramas to be constructed with no user input whatsoever.