Is it true that I’m not supposed to smile for a passport photo?

Smiling in passport photos has indeed been banned in many countries. In the U.S., guidelines state that you must have a “neutral expression” with the eyes fully open. A slight, closed-mouth smile is acceptable so long as other facial features, such as the eyes and nose, are not distorted. Many airports today used biometric scanning and facial recognition software. While distinctive biometric patterns can rarely be sufficiently distorted to prevent a match, the requirement for a “neutral expression” helps to ensure this.