Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/168f4c29c94695be3d8d7d27f8f2a598.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563