Windows Hello is a way to add easy way to sign-in to your computer using face recognition, iris recognition or finger print recognition. You can see the settings under
Start => Settings = > Accounts => Sign-in options
So if a person enabled Face recognition on your Windows 10 PC and what if identical twin of him/her tried to access the PC? See the below video, it is from Australia where they tried 6 pairs of identical twins and Windows Hello could identify them without much problems
Remember, this feature will be available for users who will have the sufficient hardware attached with their PC such as fingerprint scanner, IR cameras etc..