Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/a83ff4f891b0b31a72d1b1789d0dc099.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563