<img src="graph&channel=1&xsize=300&ysize=400">
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No you don't. You want to generate

<img src="graph?channel=1&amp;xsize=300&amp;ysize=400">
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This is HTML, so HTML entities must be escaped. The code is somewhat simple (typing this from memory, so be kind if I've made a mistake):

use URI; use HTML::Entities;
my $uri = URI->new("graph", "http");
$uri->query_form(channel => 1, xsize => 300, ysize => 400);
print "<img src=\"", encode_entities($uri->as_string), "\">";
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-- Randal L. Schwartz, Perl hacker

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
            }
        );
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