So many different concepts are baked into that (seemingly) simple question, it's hard to know what to unpack first. The web offers so many opportunities to practice selective schizophrenia, sometimes it's difficult to know where one person(ality) ends and another begins.
A few of the ways I've seen sites try to prove you are who you say you are leverage existing well-funded tracking systems:
- Leverage the credit card authentication system (simply pay US$1.00 on your credit card and we'll verify you are who you say you are). But this method assumes that 1) you have a credit card and 2) you can afford the dollar to validate your ID. Nothing wrong with this method as long as you're looking to get credit-worthy Americans who can afford to spend a buck to tell you who they are on your system.
- Leverage the banking industry by making small (talking a few dimes' worth) deposits in your bank account and asking you to verify the amounts. This method assumes that 1) you're willing to give up all your bank account information to a third party site (why is it I'm putting myself through this?) and 2) you have an account to begin with. Again, nothing wrong with this method as long as you're looking to get folks who have bank accounts (normally US banks at that) to give up their demographic info to validate they have access to accounts on your system.
More to come at a later date (yes, trying to figure out how this applies to the omidyar.net folks)