Swiss army knife of image processing
GraphicsMagick provides a set of commandline tools and programming APIs for manipulating, editing, and converting raster and vector images. It is derived from ImageMagick, with the objective of providing better stability and performance than ImageMagick while retaining the original MIT/X11 license.
A whole bunch of utilities for primitive manipulation of graphic images. Wide array of converters from one graphics format to another. E.g. from g3 fax format to jpeg. Many basic graphics editing tools such as magnifying and cropping.
Various small and useful command-line utilities
The littleutils include a duplicate file finder (repeats), image optimizers (opt-jpg, opt-png, opt-gif, recomp-jpg), file rename tools (lowercase, uppercase, pren), archive recompressors (to-gzip, to-bzip, to-7zip, to-lzma, to-lzip, to-xz), a tempfile utility (tempname), file property tools (filedate, filemode, filenode, fileown, filesize, and lrealpath), and others. See the README file for more details.
Convert Netpbm programs to GIMP plug-ins
Netpbm2Gimp automatically compiles the unmodified source code of a Netpbm graphics program into a GIMP plug-in. The result looks and functions like any other GIMP plug-in although it takes much less effort to produce than a hand-coded GIMP plug-in.
Hints for graphics conversion
Hints for conversion procedures from Fig and Gnuplot to PDF, EPS, SVG. Conversion between PDF, EPS, SVG and to PNG, JPEG, ICO, XPM. Perl script for end users invoking suitable conversion commands.