Captcha image not showing?

[eluser]PAstorKill[/eluser]
The code of captcha_lib:



<?php if (!defined('BASEPATH')) exit('No direct script access allowed');

class Captcha_lib
{
public function captcha_actions()

{
$CI = & get_instance();

$CI->load->plugin('captcha_pi');

$CI->load->helper('string');
$rnd_str = random_string('numeric',5);

$ses_data= array();
$ses_data['rnd_captcha'] = $rnd_str;
$CI->session->set_userdata($ses_data);


$settings = array ('word' => $rnd_str,
'img_path' => './img/captcha/',
'img_url' => base_url().'/img/captcha',
'font_path' => './system/fonts/LucidaBrightDemiBold.ttf',
'img_width' => 120,
'img_height' => 30,
'expiration' => 10);

$captcha = create_captcha($settings);


$imgcode = $captcha['image'];
return $imgcode;
}

}



?>


Why browser says that - Call to undefined method CI_Loader::plugin() ??????????