Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/9c996e0b5c1f74cc63ddf1998a7a8a24.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563