Abstract: A detection system assesses whether a person viewed by a computer-based system is a live person or not. The system has an interface configured to receive a video stream; a word, letter, character or digit generator subsystem configured to generate and output one or more words, letters, characters or digits to an end-user; and a computer vision subsystem. The computer vision subsystem is configured to analyse the video stream received, and to determine, using a lip reading or viseme processing subsystem, if the end-user has spoken or mimed the or each word, letter, character or digit, and to output a confidence score that the end-user is a “live” person or not.