It is very simple. You cannot use it because...well because I said so.
Chris mentioned the most important point, being that: All gfx uploaded to a graal server's ftp is supposed to become proptery of GraalOnline. And since Graal cant claim sole ownership of "public domain" gfx, it cannot upload them onto it's servers.
If you want to argue that point, realize my stance is that it wont be allowed, and so there is no point in arguing it any further..