Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/f3db20ef42e4f6d6cbfcbd3131d1a81b.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563