Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/f6a5ef4ccf0ad0e32d51f39105030c48.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563