Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/d0f6bd2bb7fe94c1b396aacc0c0d96b8.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563