Disclosed is a system for detecting a genuine user. The system may comprise a retriever, a coplanarity determiner, a constructor and a detector. The retriever may receive an image sequence of a subject including at least a first and a second image, and retrieve facial landmarks of the first and second images to form matched pairs of facial landmarks, in which each facial landmark of the first image is matched with a facial landmark in the second image. The coplanarity determiner may determine if 3D points associated with the matched pairs of facial landmarks are coplanar based on locations of the facial landmarks. The constructor may construct a 3D point cloud for the first and second images from the locations of the facial landmarks if the 3D points associated with the facial landmarks are not coplanar. The detector may detect whether the subject is a real face of the genuine user based on the constructed 3D point cloud.