See http://www.imagemagick.org
Easiest to install via your distro's package management system (eg for
Debian/Ubuntu: apt-get install imagemagik). Then use the 'convert' program to
stitch images together. (See
http://news.povray.org/povray.text.tutorials/thread/%3Cweb.52e993ec552e7103d19b0ec40%40news.povray.org%3E/).
