Captcha.php

<?php
class Captcha{
    public function generate_captcha()
    {
        $this->load->helper('captcha');
        $random_number = substr(number_format(time() * rand(),0,'',''),0,6);
        $config = array(
            'word' => $random_number,
            'img_path' => './files/captcha/',
            'img_url' => base_url().'files/captcha/',
            'img_width' => 200,
            'img_height' => 60,
            'font_path'  => './assets/fonts/burnstown_dam.ttf',//silahkan download sendiri jenis font yang anda sukai
            'font_size' => 26,
            'expiration' => 7200
        );
        $captcha = create_captcha($config);
        $this->session->set_userdata('captcha',$captcha["word"]);
        return $captcha;
    }

    public function __get($key)
    {
        return get_instance()->$key;
    }
}