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i have a web site, where we periodically launching some photo contests. also we have a group of users, who have registered lots of fake accounts for voting. this is a big problem which discredit our contests. so the question is - how to detect which user is real and which one is fake.

here some cases we've tried: 1) email verification - doesn't helps, because service like 10minutemail allows getting verification email 2) ip verification - we have a lot of ISP, which uses 1-2 IP's for all users, also a lot of companies uses one external IP. 3) voting with social networks buttons - not every our user has an account in any social network, and SN buttons allows voting only once per photo. but we want to allow voting every 24hours.

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3 Answers 3

There's really nothing much you can do about this.

Even services like Hotmail and GMail allow you to set up many accounts, so a single person may have 10 GMail accounts, 10 Hotmail accounts, etc.

If you use a cookie-based solution, that is somewhat better but a person can purge all cookies at any time and can also use different browsers. Still, I would probably choose this method because it is less unreliable than email address or IP address.

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One idea is to base registration to phone number - sure some users have more then 1 phone, but not that much as emails. You would not verify account via mail, but via sms.

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As SMS costs money, I think if credibility is really concerned, Paypal could possibly be used. One could vote for $0.01, which is I think less than the cost of an SMS, yet it offers good authentication. Of course, not everyone has a PayPal account...

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