ImageMagick is free software: it is delivered with full source code and can be freely used, copied, modified and distributed. It runs on all major operating systems.
Most of the functionality of ImageMagick can be used interactively from the command line; more often however, the features are used from progams written in the programming languages Perl, C, C++, Python or Java, for which ready-made ImageMagick interfaces (PerlMagick, Magick++, PythonMagick and JMagick) are available. This makes it possible to modify or create images automatically and dynamically.
There is no general purpose GUI front end for ImageMagick.
GraphicsMagick is a fork of ImageMagick 5.5.2 which is intended to provide a more stable interface.