Resemble.ai says that acial liveness systems analyze incoming video frames for signals that distinguish a live face from a spoofed one: Texture inconsistencies: Real skin has specific grain and light-reflection behavior. Synthetic faces often show flattened textures or irregular reflections. Micro-movements: A live face moves continuously - minor eye tremor, breathing motion, natural shifts. A static image or poorly generated face does not. Depth cues: 3D liveness systems map facial depth to confirm a real three-dimensional structure. Temporal consistency: AI-generated faces can produce frame-level artifacts - flickering, unnatural blinking, or lighting shifts inconsistent with the environment. 

Source: https://www.resemble.ai/resources/real-time-liveness-detection-solutions-for-deepfake-fraud