CI gregwar/captcha lib

<?php

use Gregwar\Captcha\CaptchaBuilder as GregwarCaptchaBuilder;

class CaptchaBuilder {

    protected $captchaSessionKey = 'captcha';
    protected $CI;
    protected $captchaBuilder;

    public function __construct() {
        $this->CI = &get_instance();
    }

    public function init($width = 150, $height = 40, $usePrevCaptcha = false) {
        $captcha = $usePrevCaptcha ? $this->getCaptchaFromSession() : null;
        $this->captchaBuilder = new GregwarCaptchaBuilder($captcha);
        $this->captchaBuilder->build($width, $height);
        $this->CI->session->set_userdata($this->captchaSessionKey, $this->captchaBuilder->getPhrase());
    }

    public function getInline() {
        return $this->captchaBuilder->inline();
    }

    public function reset() {
        $this->CI->session->unset_userdata($this->captchaSessionKey);
    }

    public function setCaptchaSessionKey($key) {
        $this->captchaSessionKey = $key;
        return $this;
    }

    public function getCaptchaSessionKey() {
        return $this->captchaSessionKey;
    }

    public function check($checkString) {
        return ($checkString == $this->getCaptchaFromSession());
    }

    public function getCaptchaFromSession() {
        return isset($this->CI->session->{$this->captchaSessionKey}) ? $this->CI->session->{$this->captchaSessionKey} : null;
    }

}