Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/cd5b8b14bbda2fbb6c6c9946b93d4de8.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563