CodeIgniter 2.0.2 CAPTCHA help / Tutorial?

[eluser]NordicElf[/eluser]
I need some help on getting the captcha helper to work. Not sure what I'm doing wrong, it only returns false! no errors, no array, just false.

On my local set up I'm running WAMP. I checked gd library is installed and activated. I tried on my host servers (linux) same story.

this is my code:

Code:

$this->load->helper('captcha');

                $vals = array(
                'img_path'  => $_SERVER["DOCUMENT_ROOT"] . 'captcha/',
                'img_url'  => site_url().'captcha/',
                'img_width'  => '200',
                'img_height' => 30,
                'border' => 0,
                'expiration' => 7200
                );
                var_dump($vals);
                 // create captcha image
                $cap = create_captcha($vals);
                var_dump($cap);

the dumps produce;

Code:

array (size=6)
  'img_path' => string 'C:/wamp/www/captcha/' (length=20)
  'img_url' => string 'http://localhost/auth_test/captcha/' (length=35)
  'img_width' => string '200' (length=3)
  'img_height' => int 30
  'border' => int 0
  'expiration' => int 7200

boolean false

I have the folders set up with permissions.

Help!