I think this is a way to go.

 The second tier would be a little harder to qualify for, and this would be those folks who want to take part in revenue sharing.   The amount of information required would go beyond just a simple email address and paypal account. Your IP would be logged (not foolproof, granted, but it cuts way down on multiple account abuses) to start with and you could not start a duplicate account from the same ip address.

An email address registered with PayPal *is* verified. Useless to fake, because you couldn't get your money out of PayPal.

Sending a code to an email address and the receiver has to enter this code into a webpage before money is sent out is another possibility to verify users.

Any dialup-user gets a new IP address every day. No chance to check this. If you have a need to make it 100%: Use a certificate (sent out via snail-mail) and SSL for upload. A bit softer: Submit Access-ID's via phone (a good way to make some extra money). Anything is better than doing something based on an IP address (I'm able to fake my IP-address while accessing a website, by the way - and I'm not a champion).