View file modules/admin_mail/antibot.php

<?php
header("Content-type: image/png");
$im = @imagecreate(47, 20)
   or die("Cannot Initialize new GD image stream");
$background_color = imagecolorallocate($im, 0, 0, 0);
$text_color = imagecolorallocate($im,255, 255, 255);
$rand = "$_GET[rand]";
imagestring($im, 4, 7, 3, "$rand", $text_color);
imagepng($im);
imagedestroy($im);
?>