Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/17e582d0fb9fc9ccb80a7dd574d7b5bf.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563