Actually, I only had to do this (still using CGI):

use CGI;
use URI;
    my $target   = URI->new( 'graph', 'http' );
    $target->query_form(
           channel => 1,
            xsize => $xsize,
            ysize => $ysize,
        );
         print $q->img(
            {
                -width  => $xsize,
                -height => $ysize,
                -src    => $target->path_query
            }
        );
[download]