What technique will provide the greatest assurance that a stolen or cloned access badge will not allow an attacker access?

Requiring a PIN is the best option unless guards are in place to validate that the person using the badge matches the badge. Even then a PIN may be better than a picture if the badge does not have other elements like holographic seals that will prevent it from being modified. Barcode and RFID badges can still be cloned and are not as effective as requiring a knowledge-based identifier as well as a possession-based identifier.