On a Debian system using the texlive distribution you need to install
the package texlive-latex-extra if you want to use the "toimage"
environment. The reason is that hevea generates for each toimage
environment a temporary TeX file that uses the "comment" environment
(provided by the texlive-latex-extra package) and then runs latex on
it to produce the image.

 -- Ralf Treinen <treinen@debian.org>  Sun, 01 Sep 2013 20:01:28 +0200