Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/2fe40c1fec6b9e8b3ff02e97a9bc83f5.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563