cake php captcha problem

Question

Hello,

I am facing problem with captcha in cake php. when try to call captcha the session value display previous one. so never get the right answer.

Here is my code.

For component section i put this code

class CaptchaComponent extends Object
{
    var $controller; 

 var $font = 'monofont.ttf';

 function CaptchaComponent( $controller ) {
  $this->controller = $controller;
 }

 function generateCode($characters) {
  /* list all possible characters, similar looking characters and vowels have been removed */
  $possible = '23456789bcdfghjkmnpqrstvwxyz';
  $code = '';
  $i = 0;
  while ($i < $characters) { 
   $code .= substr($possible, mt_rand(0, strlen($possible)-1), 1);
   $i++;
  }
  return $code;
 }

 function create($width='120',$height='40',$characters='6') {
  $code = $this->generateCode($characters);
  /* font size will be 75% of the image height */
  $font_size = $height * 0.80;
  $image = @imagecreate($width, $height) or die('Cannot initialize new GD image stream');
  /* set the colours */
  $background_color = imagecolorallocate($image, 220, 220, 220);
  $text_color = imagecolorallocate($image, 10, 30, 80);
  $noise_color = imagecolorallocate($image, 150, 180, 220);
  /* generate random dots in background */
  for( $i=0; $i<($width*$height)/3; $i++ ) {
   imagefilledellipse($image, mt_rand(0,$width), mt_rand(0,$height), 1, 1, $noise_color);
  }
  /* generate random lines in background */
  for( $i=0; $i<($width*$height)/150; $i++ ) {
   imageline($image, mt_rand(0,$width), mt_rand(0,$height), mt_rand(0,$width), mt_rand(0,$height), $noise_color);
  }
  /* create textbox and add text */
  $textbox = imagettfbbox($font_size, 0, $this->font, $code) or die('Error in imagettfbbox function');
  $x = ($width - $textbox[4])/2;
  $y = ($height - $textbox[5])/2;
  imagettftext($image, $font_size, 0, $x, $y, $text_color, $this->font , $code) or die('Error in imagettftext function');
  /* output captcha image to browser */
  header('Content-Type: image/jpeg');
  imagejpeg($image);
  imagedestroy($image);
  $this->controller->Session->write('security_code',$code);
 }
}

For user controller section my code is

function captcha() {

   App::import('Component','Captcha');
  $this->Captcha = new CaptchaComponent($this);
   $this->Captcha->create();

 }

and for view option my code is

echo $html->image('../users/captcha',  
 array('style'=>'border:1px #ccc solid','vspace'=>2)  
 );