A CAPTCHA is a system that ensures sites against bots by producing and evaluating tests that people can pass however current PC programs can't. A CAPTCHA (an acronym for "Completely Automated Public Turing test to tell Computers and Humans Apart") is a kind of test reaction test utilized as a part of registering to figure out if or not the client is human.Here is the simple way to create captcha in cakephp :-

Step 1:  Make the folder named as captcha in your project->app->Vendor. In that folder, add two folder namely fonts & Images. Also, add captcha.php file and add the following code in it :-

<?php

class captcha {	
	public function show_captcha() {
		if (session_id() == "") {
			session_name("CAKEPHP");
			session_start();
		}

		$path= VENDOR . 'captcha';
		$imgname = 'noise.jpg';
		$imgpath  = $path.'/images/'.$imgname;
		
		$captchatext = md5(time());
		$captchatext = substr($captchatext, 0, 5);
		$_SESSION['captcha']=$captchatext;

		// echo $imgpath; die;

		if (file_exists($imgpath) ){
			$im = imagecreatefromjpeg($imgpath); 
			$grey = imagecolorallocate($im, 128, 128, 128);
			$font = $path.'/fonts/'.'BIRTH_OF_A_HERO.ttf';
			
			imagettftext($im, 20, 0, 10, 25, $grey, $font, $captchatext) ;
			
			header('Content-Type: image/jpeg');
			header("Cache-control: private, no-cache");
			header ("Last-Modified: " . gmdate ("D, d M Y H:i:s") . " GMT");
			header("Pragma: no-cache");
			imagejpeg($im);
			
			imagedestroy($im);
			ob_flush();
			flush();
		}
		else{
			echo 'captcha error';
			exit;
		}		 
	}
}

 
?>

Step 2: Add the following in UsersController.php :-

App::import('Vendor', 'captcha/captcha');

 public function captcha_image(){

              $this->layout = null;
              App::import('Vendor', 'captcha/captcha');
              $captcha = new captcha();
              $captcha->show_captcha();
            }

Step  3: Add the following in login.ctp :-

echo $this->Form->input('captcha'); 
?>
</pre>
<img id="captcha" src="<?php echo $this->Html->url('/users/captcha_image');?>" alt="" />
<pre>
<a href="javascript:void(0);" onclick="javascript:document.images.captcha.src='<?php echo $this->Html->url("/users/captcha_image");?>?' + Math.round(Math.random(0)*1000) + 1" >Reset</a>
<?php

 Step 4: To check the captcha, add the following in UserController.php :-

if($this->data['user']['captcha']!=$this->Session->read('captcha'))
{
    $this->Session->setFlash(__('Please enter correct captcha code and try again.', true));
}