Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/ad2ff5a29e3c1f80574c15fa85cd3e1b.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563