What is the best way to be sure of user's identity?

Not sure this is the right stack to ask this in, it's kind of an abstract question.

Say you have a website where it is very important that the personal information provided by the users is authentic. Like age,sex, residency and optionally occupation, civil status,etc. How would you make sure that the credentials they submit are authentic? Obviously the most direct way would be requiring for the user to fax/upload scans of their certificates/IDs/etc but that would require a physical person to validate the certificates. Is there any modern, web-based way to securely connect a user's account to a physical person? Maybe like a national/global database where a person can register to(providing all the aforementioned certificates) and gets assigned a personal/unique "e-badge"?