Sometimes captcha generates an error if the session is accessed after there is some output in the response. From now on the captcha phrase will be saved first and then there will be the image output.

src/application/controllers/captcha.php

@@ -32,8 +32,9 @@ class Captcha extends CI_Controller {
     public function index() {
         header('Content-type: image/jpeg');
         $builder = new Gregwar\Captcha\CaptchaBuilder;
-        $builder->build()->output();
+        $builder->build();
         $this->session->set_userdata('captcha_phrase', $builder->getPhrase());
+        $builder->output();
     }
 }