If you think having your picture taken for a driver's license is stressful, try having your image captured for passport photos under a new set of rules enacted after the events of September 11th, 2001. Indeed, smiling in passport photos has indeed been banned in a number of countries. Passport applicants can be asked to pose for a new photo if the first one is deemed too distorted by the act of smiling.

The rules against smiling in passport photos do have some exceptions and clarifications, however. A closed mouth smile or grin is generally acceptable, but a smile which exposes the teeth is not. A grimacing "smile" formed with a closed jaw may be tolerated as long as other facial features such as the eyes and nose are not distorted unnaturally. It is primarily the open mouth, tooth-filled smile which has become problematic.

The reason smiling in passport photos has been strongly discouraged or banned has to do with international security measures. Many modernized airports now use advanced biometric scanning devices which contain facial recognition software. Ideally, a targeted passenger's face can be scanned electronically and compared against a database of legally obtained passport photos. Distinctive biometric patterns, such as the distance between one's eyes or the shape of one's mouth, can rarely be sufficiently altered to prevent a match.

The passport photographs used for comparison should ideally be consistent and accurate, with no shadows or reflections to distort the facial measurements. Passport applicants must also sweep any hair away from their faces, place their eyeglasses on the tip of their nose, and face completely forward with a neutral expression. Smiling in passport photos can distort the subject's eyes and change the relationship between biometric points.

Although the temptation to smile for a more flattering photograph may always be there, don't be surprised if the photographer pointedly asks you not to do it. Your passport photo may be unflattering, but a smile may be a small sacrifice to make in exchange for increased personal safety.