The present teaching relates to method, system, medium, and implementations for authenticating a user. An authentication session is initiated to authenticate, via iris, a person claiming to be an authorized user. A trajectory is determined with respect to a display visible to the person. A plurality of focus dots are generated with corresponding coordinates on the trajectory with respect to the display and rendered to the person on the display in accordance with the corresponding coordinates during a specified period of time. A plurality of pictures of the iris of the person are captured during the period of time and used to determine whether the person is live based on the captured plurality of pictures of the iris of the person.