Guards at U.S.-Mexico border crossings identify SENTRI cardholders using facial-recognition technology.

Dennis Poroy/Associated Press

Passport Photos

Passport photographs must be 2 inches by 2 inches in size, identical and taken within the past six months. The image size from the bottom of the chin to the top of the head should be between 1 inch and 1 3/8 inches. They may be in color or black-and-white, full face or front view, with a plain white or off-white background. (Don't worry -- professional passport photographers know these rules!) Photographs should be taken in normal street attire, without a hat or headgear that covers the hair or hairline. Uniforms should not be worn in photographs with the exception of religious attire that is worn daily. If prescription glasses, hearing aids, wigs or other such articles are normally worn, they should be worn when the picture is taken. Dark glasses or nonprescription glasses with tinted lenses are not allowed unless they are required for medical reasons. A medical certificate may be required to support the wearing of these glasses in photographs. Vending machine photos are not generally acceptable -- to be on the safe side, you'd better get a professional to take your photo and print it. (Kinko's, Eckerd's and other quick-photo places will make your photos for you while you wait. It usually costs about $15 for one shot, two prints.)