Does anybody have any ideas on how it would be possible to validate someone as a real person while maintaining their anonymity. I had the idea of them validating themselves using a debit/credit card(without a sale). Two problems there. People often have more than one card. People might think I'm phishing for their card details.

Image verification? You mean against spam or something?

No mate. I want users to remain anonymous. I don't even want their email addresses. But I want to find a way to stop multiple registrations by the same person. Given that a number of users might need to use the same computer, I'd like each user to have some way to validate themselves as a real person, from a real address, without giving me any personal identifying details.
I don't think it can be done but I'm wondering if anybody has any ideas.

I think you are right about it being impossible. In order to identify a specific person you need at least one unique identifying element. By making registration completely anonymous you take away all of these things.

Just out of curiosity what exactly is the purpose of having this completely anonymous? Might give us some ideas as to what you can do to identify seperate people.

I reckon the users are going to have to 'register', even if that means a server-side script giving them a unique id number or something rather than their choosing an alias.

But registering doesn't mean a loss of anonymity at all. Registration might just mean something like filling out a form (one which, as best you can, insures it's a real person), and generates a login number for them ... maybe they can choose a password then ... but I guess you don't want login stuff ... just a foolproof 'ishuman' function

>> want to find a way to stop multiple registrations by the same person
Even with all the personal info you might want you can't ensure this! I mean all someone has to do is create another email account and use that, for example, in daniweb. Make up a username. And hey presto. Multiple accounts. IP or mac address filtering won't work either as, as you said, more than one person might use the same computer.

>> I'm wondering if anybody has any ideas.
Fingerprints or retina scans ... I'm only guessing but I don't think you want that.

lasher,
If you follow the link in my signature, you'll see the site is a site based on direct democracy. It covers every inhabited country in the world. A lot of countries could be said to be anti-democratic and contributing to such a site could be dangerous for some users. Even in so-called democracies voting is supposed to be secret.
To answer twomers aswell, I already have an anonymous login. I also collect the users general area of residence: country, state, county, etc. This means I can count votes for a particular administrative division and sort posts into the relevant categories but users personal, identifying details are unknown to the site. It also absolves me of any data protection issues.
As the site is in its infancy and registrations are just ticking over, at the moment I can monitor all registrations. I have been able to spot one attempt at multiple registration by a single user, but should the amount of registrations increase this may become harder to do.

Digital picture of the right hand (palm) so you can see the line pattern.

>> Digital picture of the right hand (palm) so you can see the line pattern.
That's hardly convenient though. I'm guessing the OP doesn't want to put the users out lest he discourage them from participating.

Ask them to send you a $20 bill, that you will store under their username and password.