1999.10.01 10:41 "Re: JBIG in TIFF?", by Ivo Penzar
Apparently it's legal since there is a jbig library under the GPL: ftp://ftp.informatik.uni-erlangen.de/pub/doc/ISO/JBIG/
I assume it wouldn't be around and ImageMagic wouldn't be using it if there were legal problems.
Unfortunately you assume wrong. The developer of that free JBIG code is outside the US and is blithely ignoring the patent issue. If you use his code in the US then you need to worry about securing the appropriate patent licenses.
JBIG has at least the same patent problems as arithmetic-coded JPEG (patents owned by IBM, AT&T, and Mitsubishi, if memory serves) and may have some more all its own.
To be honest, libtiff itself (developed in the States), open-sourced as well, comes with support for LZW (read-write) which is copyrighted, too.