The open source environment and Linux offers some great image/graphic software useful to designers. Every tool is useful in its unique way hence providing something for each user. The cool thing is that they are free; hence, possible for you to use all them to find the one that suits you.
Inkscape
This open source and free application is editor for vector graphics. Inkscape aim involves implementing complete support for SVG (Scalable Vector Graphics) 1.1 standard. This application runs on various platforms including OS X, MS Windows and Unix-like OS.
DuhDraw
Ben Fowler developed this application and Pekka Enberg maintains it as an open source and Linux-based clone for TheDraw, which is an ASCII editor of art based on DOS. 2.7.9 is its latest version.
ImageMagick
This open source and free software suite is useful in presenting, editing and converting images files in raster. ImageMagick is bale to write and read more than 200 file formats for image. The application mainly incorporates interface utilities in command line in manipulating images. The application lacks robust GUI for editing images like that in GIMP and Adobe Photoshop, but it includes essential native X window to render and manipulate images as well as API libraries useful in various programming languages.
PicBook
This application automatically generates photo album using HTML format for your images. PicBook incorporates automatic processing of images, transition effect and slideshow among other ingenious stuff. PicBook is simple to customize because of HTML-templates and configuration file.
Xfig
This open source and free editor of vector graphics runs in X Window System in many platforms that are compatible to UNIX. Xfig supports drawing of objects like boxes, circles, text, spline curves etc. the application supports importation of images in various formats like EPS, JPEG, PostScript, GIF, etc. The application allows objects to be developed, created, modified or moved.
XPaint
This open source ad free application for editing images is useful in bitmap images in X Window within Unix-like OS. XPaint goal involves being simple and lightweight to be able to exploit the editor for raster graphics.
Xv
John Bradley develops xv as a shareware application for displaying and modifying digital images in X Window System. The application can run from both command line and GUI. xv differentiates itself from other application for editing and viewing bitmap images with efficient interface through which the user edits only the parameters in the processing steps instead of modifying directly the bitmap in every operation. Therefore, the user is easily able to undo operations (like filtering, cropping, color modifications) in any order instead of only undoing the last operation.