In addition to clothing color, passport applicants must pay attention to their facial expression. Many countries require that applicants maintain a neutral expression with their mouth closed and eyes clearly visible. Smiling or keeping the mouth open can alter the proportions of the face, which affects biometric accuracy. According to Karolina Turowska, a biometric photography specialist at Passport-Photo.Online, facial recognition algorithms measure precise distances between key features such as the pupils, nose, ears, and mouth. When a person smiles or opens their mouth, these proportions shift slightly, making it harder for machines to verify identity.
