Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/6f1180a214f35f3d2b97cab3faf2bc9d.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563