At the BBC, sci-fi writer Elizabeth Moon suggests humans get bar codes at birth:

“If I were empress of the Universe I would insist on every individual having a unique ID permanently attached – a barcode if you will; an implanted chip to provide an easy, fast inexpensive way to identify individuals.

It would be imprinted on everyone at birth. Point the scanner at someone and there it is.

Having such a unique barcode would have many advantages. In war soldiers could easily differentiate legitimate targets in a population from non combatants.”