Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/a3de56a3f40d0ebaf7ac51a6c07db1c3.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563