Mine

<?php

Header("Content-Type: image/png");
session_start();
$random;
session_register('random');
$imagec = imagecreate(100, 100);

$white = imagecolorallocate($imagec, 255, 255, 255);
$black = imagecolorallocate($imagec, 0, 0, 0,);

srand((double)microtime()*10000000);

$string = md5(rand(0,99999));
$random = subtr($string, 17, 5);
imagefill($imagec, 0, 0, $black);
imagestring($imagec, 4, 70, 10, $random, $white);
imagepng($imagec, "verification.png");
imagedestroy($imagec);


echo '<img src="verification.png">';
echo '<br><br>';
echo 'Type the code you see in the image in the box below. (case sensitive)';
echo  '<form action="verify.php" method="post">';
echo '<input name="random" type="text" value="">';
echo '<input type="submit">';
?>


</form>