Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/639070c8f1962e8b88b8e863b4579fc2.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563