1. GIMP – The GNU Image Manipulation Program
GIMP is an acronym for GNU Image Manipulation Program. It is a freely distributed program for such tasks as photo retouching, image composition and image authoring. It has many capabilities. It can be used as a simple paint program, an expert quality photo retouching program, an online batch processing system, a mass production image renderer, an image format converter, etc. GIMP is expandable and extensible. It is designed to be augmented with plug-ins and extensions to do just about anything. The advanced scripting interface allows everything from the simplest task to the most complex image manipulation procedures to be easily scripted. GIMP is written and developed under X11 on UNIX platforms. But basically the same code also runs on MS Windows and Mac OS X.
2. digiKam
digiKam is an advanced digital photo management application for Linux, Windows, and Mac-OSX. 
The people who inspired digiKam’s design are the photographers like you who want to view, manage, edit, enhance, organize, tag, and share photographs under Linux systems.
3. Fotoxx
Fotoxx is a free open source Linux program for photo editing and collection management. The goal is to meet most user needs while remaining fast and easy to use. 
Navigate a large image collection with a thumbnail browser, click on images to view or edit. Import camera RAW files and edit with 16-bit color. Save edited images as TIFF-8/16, PNG or JPEG with adjustable compression. Edit the whole image or a selected area, with smooth edge-blending. Edit functions have live feedback using the full window. Add tags, dates, star-ratings, comments and captions to images and search using these criteria plus image file names. Fotoxx uses your image files wherever they are. All user-supplied image data (tags, comments, ratings) is saved inside the image files in a standards-compliant manner (EXIF, IPTC), and can be shared with other photo programs. Fotoxx maintains an index of searchable attributes for nearly instantaneous searching.
4. Splashup Light 1.0 By Faux Labs
Taking some cues from Splashup, Splashup Light also has powerful tools for advanced image editing enthusiasts like Levels, Hue – Saturation and Brightness – Contrast. Together with standards tools like rotate, crop, resize and many fun effects, Splashup Light is a well-rounded photo editor perfect for those that don’t need or want heavy desktop image editing suites.
5. Shotwell 0.8.1 Open source photo manager for GNOME by Yorba Foundation
Shotwell is a digital photo organizer that runs on Linux. It is the default photo manager in Ubuntu 11.04 and Fedora 15.
Shotwell 0.10 is here! Major new features include:
- Dynamic views of photo library through saved searches
- Integrated video thumbnailer, eliminating Totem dependency
- Adjustable date/time for videos
- More flexible crop tool
- Automatic database backup
- Automated testing framework
6. Pencil 0.4.4b
Pencil is an animation/drawing software for Mac OS X, Windows, and Linux. It lets you create traditional hand-drawn animation (cartoon) using both bitmap and vector graphics. Pencil is free and open source.
7. Gnome Paint 0.4.0 by Rogério Ferro do Nascimento
Gnome-paint is a simple, easy to use paint program for GNOME. It is inspired by MS-Paint.
8. F-Spot Photo Manager
F-Spot is a cross platform application for organizing thousands of photos. It shuns ‘organizing in folders.’ instead, metadata is the basis for viewing and drilling down the collection. Adding and maintaining metadata is easy and enjoyable in F-Spot.
Individual photos can be retouched and globally corrected (e.g. dynamic range, color), for sharing via the net, printing and viewing by consumers. The number and sophistication of the correction scales to the the ambition of users. An advanced form of corrections is that of batches of photos.
Beginners in the digital photo field can easily start using F-Spot. These and more advanced users are encouraged by F-Spot to grow their skills, to the point where they integrate more specialized photo manipulation software into their F-Spot workflow.
