You cannot verify a passport number as a private citizen. There are things you can do to spot a false identity document, such as checking the number of digits in the passport number, but only a government official can validate the legitimacy of a passport. … Most “fake” passports are issued by the State Department.
There are several ways to tell. Law Enforcement Officers many times get updates on what to look for in all type of credentials. Not only are there things to look for but the process of making them is similar to currency. Special materials are used that can’t be found except at the genuine locations that make them. There are lamination procedures and engravings that are set in a complicated process. Just as its hard to duplicate the KFC recipe or borrow U.S. $100 dollar mint plates it’s like trying to rob Fort Knox.