Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/15dd76f3c0a9f37e417d7ff8d37833fd.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563