Help with authenticating computers

[eluser]gvillavizar[/eluser]
Hello everyone.

I need to make a votation script for a site, but I don't want to make a registration system just for voting, since I am giving prizes to the person with the most votes I need to restrict votation to only one per day.

I tried doing it and storing the IP address, so no one will vote from that IP and in the midnight a cron will erase the ip in the database so it can vote again for that day...that worked out great until I came to the realization that computer networks share the same ip. So if I want my coworkers to vote for me only one of them will be able to.

I don't want to make it via a cookie because that can be violated, clearing cookies and then voting again.

What I need to do is match the computer in the network specifically so a computer can vote once each day but two computers with the same ip can vote the same day.

I though of using the useragent aswell, but that will give me a user with 4 browsers to be able to vote for one person, and in the same network people can use the same browser so that will be the ip problem all the way down.

You have any suggestion on how I can accomplish this?

Thank in advance.

[eluser]mdvaldosta[/eluser]
If users don't register, how are you going to be able to track who has the most votes? IP addresses can change, cookies can be erased, etc. I'm just curious. Without registration, I see now real way to be able to consistantly track someone. Perhaps you can make an "auto" registration where once they input their username a check is made to see if already exists, if not it's made. Then store votes per username in the database, and use that to enforce the voting limitations.