Disclosed herein are methods and systems for determining whether a user engaged in an interactive video session is a genuine user or a potential impersonator by analyzing a plurality of consecutive images depicting the user while engaged in the video session to identify one or more dynamic facial patterns in the face of the user while his lips are moving. Each such dynamic facial pattern may express a movement of one or more of a plurality of wrinkles and/or other dynamic facial features (e.g., nostrils, distance between nostrils, ear, skin portion, muscle, etc.) in the face of the user. The user may be then determined to be genuine or not based on a comparison between the identified dynamic facial pattern(s) and one or more reference dynamic facial patterns.