Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/21e2e2f58dc010f9ecf0dad3129505e4.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563