It is possible to verify that a user is a specific human. It is not possible to verify that a user is a vague-but-unique human. Between bots, account farming,

It is possible to verify that a user is a specific human. It is not possible to verify that a user is a vague-but-unique human. Between bots, account farming, etc. it is simply not possible any more. Legal and other requirements may prevent you from checking a drivers' license, national ID card, credit card ... but that is the only approach that can work.