//////////////// CODE.PHP ////////////////
<?php
session_start();

$tekens = 'AbCDeFgHiJklmNoPQrStUvWXyZ1234567890';
$code = '';

for ($i=0; $i<3; $i++)
{
	$code .= $tekens {rand (0, strlen ($tekens) - 1)};
}

$_SESSION["auth_code"] = $code;

header("Content-type: image/png");

$image = imagecreatetruecolor(90, 50);
$back = imagecolorallocate($image, 212, 238, 255);
$black = imagecolorallocate($image, 0, 0, 0);
$red = imagecolorallocate($image, 255, 0, 0);

imagefill($image, 0, 0, $back);
imagerectangle($image, 0, 0, 89, 49, $black);

for ($i = 0; $i <= 50; $i+=5)
	imageline($image, mt_rand($i,$i+40), 0, mt_rand($i,$i+40), 50, $black);

for ($i = 0; $i <= 90; $i+=5)
	imageline($image, 0, mt_rand($i,$i+30), 90, mt_rand($i,$i+30), $black);

imagettftext($image, 20, rand(-20, 20), 15, 30, $red, "codefont.ttf", $code);
imagepng($image);
imagedestroy($image);
?>

//////////////// TESTFORM.PHP ////////////////
[code]<?php
if($_SERVER["REQUEST_METHOD"] == "POST") {
	session_start();
	if($_SESSION["auth_code"] == $_POST["code"])
		echo "Code goed!";
	else
		echo "Code fout!";
}
?>
<form method="post" action="<?php echo $_SERVER["PHP_SELF"] ?>">
<img src="code.php"><br>
Code: <input type="text" name="code" size=5><input type="submit" value="Zend!">
</form>[/code]