Smart ID is the web service that allows you to find out the real identity of your website users.
This service originates from Estonia where national ID cards with smart card chip has been used over 15 years and hundreds of public and private services are using it to identify and login users to their systems. Short list of more popular services can be found from http://www.id.ee/index.php?id=30230
Smart ID has implemented many different identification methods to identify people because each country has its own popular methods and this list just keeps on growing. Currently it is possible to identify people Securely in Estonia, Latvia, Lithuania and Portugal.
Each method has its own security level. National ID cards with smart cards are considered one of the most secure. Similar are also some mobile solutions where certificates are on the sim cards like Estonian and Lithuanian Mobile-ID.
In many countries banks provide identification services with 2-factor-authentication (2FA) like pin calculators, code cards or SMS messages to phones.
Finally there are password based methods like Facebook and Google login. These do not tell you person real identity but if these are connected to any methods that tells you identity then later it is possible to identify people using Facebook and Google also.
Password based methods main disadvantage is that passwords can be copied secretly. Have you seen any of your friends Facebook account taken over? Of course you have!
Password based methods also may or may not have 2FA. Google has this option where during every login or in every new computer you have to enter code from your phone.
Information of which electronic identity cards are available in different countries can be found from https://smartid.ee/countries-available-smart-card-identifications-methods/.