How will ESL enforce this?
Will you be asking all participants for proof of citizenship or will it only be players who win prizes be requested to submit proof?
What forms of ID are acceptable? bearing in mind a high percentage of people from the USA do not have passports.
State Drivers license or military ID would be alternative ID choices. For proof of citizenship birth certificate is the only thing I can think of, I'm sure many wouldn't be willing to send pictures of that to others though. And honor system wouldn't work because people would lie. What about those with dual citizenship? I'm interested to hear what ESL has to say.