The [[plugins/teximg]] plugin currently has a TODO in the source code to make the preamble configurable.  The included [[patch]] makes this change.

The patch also makes some other changes:

  - The default latex preamble is changed to the international standard `article` class from the European `scrartcl` class.
  - Removed the non-standard `mhchem` package from the default preamble.
  - Allow the use of `dvipng` rather than `dvips` and `convert` (`convert` is not a standard part of a latex install).  This is configurable.

-- [[Will]]

    diff --git a/IkiWiki/Plugin/teximg.pm b/IkiWiki/Plugin/teximg.pm
    index 369c108..8c3379f 100644
    --- a/IkiWiki/Plugin/teximg.pm
    +++ b/IkiWiki/Plugin/teximg.pm
    @@ -10,6 +10,18 @@ use File::Temp qw(tempdir);
     use HTML::Entities;
     use IkiWiki 2.00;
     
    +my $default_prefix = <<EOPREFIX
    +\\documentclass{article}
    +\\usepackage{amsmath}
    +\\usepackage{amsfonts}
    +\\usepackage{amssymb}
    +\\pagestyle{empty}
    +\\begin{document}
    +EOPREFIX
    +;
    +
    +my $default_postfix = '\\end{document}';
    +
     sub import { #{{{
     	hook(type => "getsetup", id => "teximg", call => \&getsetup);
     	hook(type => "preprocess", id => "teximg", call => \&preprocess);
    @@ -21,6 +33,26 @@ sub getsetup () { #{{{
     			safe => 1,
     			rebuild => undef,
     		},
    +		teximg_dvipng => {
    +			type => "boolean",
    +			description => "Should teximg use dvipng to render, or dvips and convert?",
    +			safe => 0,
    +			rebuild => 0,
    +		},
    +		teximg_prefix => {
    +			type => "string",
    +			example => $default_prefix,
    +			description => "LaTeX prefix for teximg plugin",
    +			safe => 0, # Not sure how secure LaTeX is...
    +			rebuild => 1,
    +		},
    +		teximg_postfix => {
    +			type => "string",
    +			example => $default_postfix,
    +			description => "LaTeX postfix for teximg plugin",
    +			safe => 0, # Not sure how secure LaTeX is...
    +			rebuild => 1,
    +		},
     } #}}}
     
     sub preprocess (@) { #{{{
    @@ -105,25 +137,34 @@ sub gen_image ($$$$) { #{{{
     	my $digest = shift;
     	my $imagedir = shift;
     
    -	#TODO This should move into the setup file.
    -	my $tex = '\documentclass['.$height.'pt]{scrartcl}';
    -	$tex .= '\usepackage[version=3]{mhchem}';
    -	$tex .= '\usepackage{amsmath}';
    -	$tex .= '\usepackage{amsfonts}';
    -	$tex .= '\usepackage{amssymb}';
    -	$tex .= '\pagestyle{empty}';
    -	$tex .= '\begin{document}';
    +	if (!defined $config{teximg_prefix}) {
    +		$config{teximg_prefix} = $default_prefix;
    +	}
    +	if (!defined $config{teximg_postfix}) {
    +		$config{teximg_postfix} = $default_postfix;
    +	}
    +	if (!defined $config{teximg_dvipng}) {
    +		# TODO: Can we detect whether dvipng or convert is in the path?
    +		$config{teximg_dvipng} = 1;
    +	}
    +	
    +	my $tex = $config{teximg_prefix};
     	$tex .= '$$'.$code.'$$';
    -	$tex .= '\end{document}';
    +	$tex .= $config{teximg_postfix};
    +	$tex =~ s!\\documentclass{article}!\\documentclass[${height}pt]{article}!g;
     
     	my $tmp = eval { create_tmp_dir($digest) };
     	if (! $@ &&
    -	    writefile("$digest.tex", $tmp, $tex) &&
    -	    system("cd $tmp; latex --interaction=nonstopmode $tmp/$digest.tex > /dev/null") == 0 &&
    -	    system("dvips -E $tmp/$digest.dvi -o $tmp/$digest.ps 2> $tmp/$digest.log") == 0 &&
    -	    # ensure destination directory exists
    -	    writefile("$imagedir/$digest.png", $config{destdir}, "") &&
    -	    system("convert -density 120  -trim -transparent \"#FFFFFF\" $tmp/$digest.ps $config{destdir}/$imagedir/$digest.png > $tmp/$digest.log") == 0) {
    +		writefile("$digest.tex", $tmp, $tex) &&
    +		system("cd $tmp; latex --interaction=nonstopmode $tmp/$digest.tex > /dev/null") == 0 &&
    +		# ensure destination directory exists
    +		writefile("$imagedir/$digest.png", $config{destdir}, "") &&
    +		(($config{teximg_dvipng} &&
    +			system("dvipng -D 120 -bg Transparent -T tight -o $config{destdir}/$imagedir/$digest.png $tmp/$digest.dvi > $tmp/$digest.log") == 0
    +			) || 
    +		(!$config{teximg_dvipng} &&
    +			system("dvips -E $tmp/$digest.dvi -o $tmp/$digest.ps 2> $tmp/$digest.log") == 0 &&
    +			system("convert -density 120  -trim -transparent \"#FFFFFF\" $tmp/$digest.ps $config{destdir}/$imagedir/$digest.png > $tmp/$digest.log") == 0))) {
     		return 1;
     	}
     	else {