Captcha in cakephp

When we build websites with forms their emerge situatiion where we want to include captcha to prevent it from spammers. here iam including a captcha controller which can be used in cakephp.
<?php

class CaptchaController extends AppController{

public $uses = array('SessionManager','Validator','Captcha','Flash');
public $components=array('Session');

function init(){
$this->SessionManager->Session=$this->Session;
}
function index(){
$this->init();
/*
$text = $this->SessionManager->get('captchaText');
$height = 25;
$width = 65;

$image_p = imagecreate($width, $height);
$black = imagecolorallocate($image_p, 0, 0, 0);
$white = imagecolorallocate($image_p, 255, 255, 255);
$font_size = 14;
ob_start();
imagestring($image_p, $font_size, 5, 5, $text, $white);
imagejpeg($image_p, null, 80);
exit;*/

$urlRoot=Router::url('/',false);
$image_width = 120;
$image_height = 35;
$characters_on_image = 6;
$dir = Configure::read('FondDir');
$font = $dir.'/monofont.ttf';
$possible_letters = '23456789bcdfghjkmnpqrstvwxyz';
$random_dots = 0;
$random_lines = 20;
$captcha_text_color="0x142864";
$captcha_noice_color = "0x142864";
$code = '';
$i = 0;
ob_start();
while ($i < $characters_on_image) {
$code .= substr($possible_letters, mt_rand(0, strlen($possible_letters)-1), 1);
$i++;
}
$this->SessionManager->set('captcha',$code);
$this->Session->write('captcha',$code);
$font_size = $image_height * 0.75;
$image      = @imagecreate($image_width, $image_height);


/* setting the background, text and noise colours here */
$background_color = imagecolorallocate($image, 255, 255, 255);

$arr_text_color = $this->hexrgb($captcha_text_color);
$text_color = imagecolorallocate($image, $arr_text_color['red'],
$arr_text_color['green'], $arr_text_color['blue']);

$arr_noice_color = $this->hexrgb($captcha_noice_color);
$image_noise_color = imagecolorallocate($image, $arr_noice_color['red'],
$arr_noice_color['green'], $arr_noice_color['blue']);


/* generating the dots randomly in background */
for( $i=0; $i<$random_dots; $i++ ) {
imagefilledellipse($image, mt_rand(0,$image_width),
mt_rand(0,$image_height), 2, 3, $image_noise_color);
}


/* generating lines randomly in background of image */
for( $i=0; $i<$random_lines; $i++ ) {
imageline($image, mt_rand(0,$image_width), mt_rand(0,$image_height),
mt_rand(0,$image_width), mt_rand(0,$image_height), $image_noise_color);
}


/* create a text box and add 6 letters code in it */
$textbox = imagettfbbox($font_size, 0, $font, $code);
$x = ($image_width - $textbox[4])/2;
$y = ($image_height - $textbox[5])/2;
imagettftext($image, $font_size, 0, $x, $y, $text_color, $font , $code);


/* Show captcha image in the page html page */
header('Content-Type: image/jpeg');// defining the image type to be shown in browser widow
imagejpeg($image);//showing the image
imagedestroy($image);//destroying the image instance


exit;
}

function hexrgb ($hexstr)
{
 $int = hexdec($hexstr);

 return array("red" => 0xFF & ($int >> 0x10),
  "green" => 0xFF & ($int >> 0x8),
  "blue" => 0xFF & $int);
}


}

?>
and after including this in your controller page .. so after that you have to call captchja somewhere so you can call like this
img src="<?php echo  $urlRoot;?>captcha/" alt="Captcha Security Code" class="captcha" />


and in the action file where you want to get this value,simply call like this
$captcha = $this->SessionManager->get('captcha');

and you can check the captcha value with the user entered captcha value and can submit the form..