Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/0cef1aff2fbe06b4cfe59d0902b6cc0e.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563