CVV2: A new Three-Digit Value: An important new security feature for card-not present transactions now appears on the back of most Visa, Mastercard and Discover cards. This new feature is a three-digit value which provides a cryptographic check of the information embossed on the card.
CVV2's Location: The CVV2 three-digit value is printed on the signature panel on the back of Visa, Mastercard, or Discover cards immediately following the card account number.
The Card Identification # is the 4 digit, non-embossed number printed above your account number on the face of your card. This number is recorded as an additional security precaution.
If your AMEX account number does not have a plastic card associated with it, then you do not have a Card Identification #. In this case, you should enter the last 4 digits of your AMEX account number in the Card Identification # field in order for your transaction to be processed.
These values help validate two things: