Authenticator card with changing bar code pattern

An authenticator card includes a liquid crystal display arranged to exhibit a dynamically changeable bar code pattern that represents an account number and, optionally, a PIN and/or expiration date. The card includes circuitry for periodically changing the bar code in accordance with a predetermined algorithm. When the card is presented by a user to a merchant to authenticate the identity of the user in connection with a business transaction, the bar code is scanned by a conventional bar code reader. The code is converted to electronic form and transmitted to a verification processor to be authenticated. During authentication, a corresponding algorithm is used to validate information from the received signal, enabling a database query to determine validity of the card. Advantageously, the card can be mass produced at low cost, and a readily available bar code scanner provides a simple interface when the card is presented for authentication.