Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/6de0bbc21b94e462ea085e4f03ad6817.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563