ImageMagick is a library for creating and manipulating bitmap images and supports a wide variety of file formats.
lisp-magick requires cffi and should work on any CL implementation supported by it. However, so far only SBCL and CLISP have been tested.
So far there isn't much documentation about lisp-magick, but you can use the MagickWand C-API documentation. The lisp-magick homepage has a few simple examples.