Log IP address of users / block registration

[eluser]taewoo[/eluser]
U can combination of

1) cookies
2) IP

... which is equivalent of saying use a DB session.

As far as people circumventing IP via spoofing.. 99.9% of the world's population doesn't understand so you don't need to worry too much. If they're trying to game your system, then hopefully by then, your site is popular ... which means $$$.. which means u can hire people to do that.

Internet was designed for anonymity. Even Google can't ALWAYS tell who you are unless you have logged in at least once.

Moral of the story: clear your cookies