Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/21d1251a1727ec87660e0a84f4eb79c2.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563