Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/31e6fadb6d704beadb8b8c5c02dd6d16.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563