Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/ca5c0efe2f0a6e2df21a635a8f81713c.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563