This helper is loaded using the following code:

In Controller itself(* can repeat again and again*)

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

In config/autoload.php (Load only once)

$autoload['helper'] = array('captcha');

Takes an array of information to generate the CAPTCHA as input and creates the image to your specifications, returning an array of associative data about the image.

[array]
(
  'image' => IMAGE TAG
  'time'    => TIMESTAMP (in microtime)
  'word'    => CAPTCHA WORD
)

The "image" is the actual image tag:

<img src="http://example.com/captcha/12345.jpg" width="140" height="50" />

The "time" is the micro timestamp used as the image name without the file extension. It will be a number like this: 1139612155.3422

The "word" is the word that appears in the captcha image, which if not supplied to the function, will be a random string.

Once loaded you can generate a captcha like this:

$vals = array(
    'word'    => 'Random word',
    'img_path'    => './captcha/',
    'img_url'    => 'http://example.com/captcha/',
    'font_path'    => './path/to/fonts/texb.ttf',
    'img_width'    => '150',
    'img_height' => 30,
    'expiration' => 7200
    );

$cap = create_captcha($vals);
echo $cap['image'];

• The captcha function requires the GD image library.
• Only the img_path and img_url are required.
• If a "word" is not supplied, the function will generate a random ASCII string. You might put together your own word library that you can draw randomly from.
• If you do not specify a path to a TRUE TYPE font, the native ugly GD font will be used. The "captcha" folder must be writable (666, or 777)
• The "expiration" (in seconds) signifies how long an image will remain in the captcha folder before it will be deleted. The default is two hours.

Here is an example of usage with a database. On the page where the CAPTCHA will be shown you'll have something like this:

$this->load->helper('captcha');
$vals = array(
    'img_path'    => './captcha/',
    'img_url'    => 'http://example.com/captcha/'
    );

$cap = create_captcha($vals);

$data = array(
    'captcha_time'    => $cap['time'],
    'ip_address'    => $this->input->ip_address(),
    'word'    => $cap['word']
    );

$query = $this->db->insert_string('captcha', $data);
$this->db->query($query);

echo 'Submit the word you see below:';
echo $cap['image'];
echo '<input type="text" name="captcha" value="" />';

Then, on the page that accepts the submission you'll have something like this:

// First, delete old captchas
$expiration = time()-7200; // Two hour limit
$this->db->query("DELETE FROM captcha WHERE captcha_time < ".$expiration);  

// Then see if a captcha exists:
$sql = "SELECT COUNT(*) AS count FROM captcha WHERE word = ? AND ip_address = ? AND captcha_time > ?";
$binds = array($_POST['captcha'], $this->input->ip_address(), $expiration);
$query = $this->db->query($sql, $binds);
$row = $query->row();

if ($row->count == 0)
{
    echo "You must submit the word that appears in the image";
}