Select Code to Download

my $msg  = sha1_base64(
    join("^G", ("secret part", map {$cgi->param($_)} 
        grep {not m/^(?:usec|utime|tcode)$/} $cgi->param)));

my $code = $1 if $msg =~ m/(.{4})\z/;

print $cgi->header({type=>"image/png"});

...
}

print $gd->png;