Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/ca7f8f322f8f0787d8d6493d5f7b6df7.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563