A computer-implemented method, for verifying an electronic device user, comprising the steps of: issuing at least one action instruction to an electronic device user using a notification mechanism of the electronic device; recording response data from a plurality of data acquisition systems of the electronic device, the response data pertaining to the user's response to the at least one action instruction; processing the response data to form classification scores by processing the response data to identify the likelihood of at least one characteristic pattern associated with an action instruction, combining the classification scores to form a classification value; and verifying the user if the classification value satisfies a threshold, wherein each of the at least one action instructions comprises a liveness challenge, to check liveness of the user, wherein the plurality of data acquisition systems comprises a first data acquisition system and a second data acquisition system, wherein the first data acquisition system is different to the second data acquisition system, wherein at least one action instruction comprises an audio challenge and a motion challenge, wherein the audio challenge comprises an instruction to say at least one word, and wherein the motion challenge comprises an instruction to perform at least one motion, wherein the at least one motion comprises a head motion, wherein the step of processing the response data comprises processing video data to assess the classification score of at least one characteristic motion associated with the action instruction, wherein processing video data comprises performing facial action recognition on the video data, and wherein performing facial action recognition on the video data comprises: performing a plurality of head pose estimations on the video data; processing the plurality of head pose estimations to form extracted pose information; and forming a facial action classification score using the extracted pose information. issuing at least one action instruction to an electronic device user using a notification mechanism of the electronic device; recording response data from a plurality of data acquisition systems of the electronic device, the response data pertaining to the user's response to the at least one action instruction; processing the response data to form classification scores by processing the response data to identify the likelihood of at least one characteristic pattern associated with an action instruction, combining the classification scores to form a classification value; and verifying the user if the classification value satisfies a threshold, wherein each of the at least one action instructions comprises a liveness challenge, to check liveness of the user, wherein the plurality of data acquisition systems comprises a first data acquisition system and a second data acquisition system, wherein the first data acquisition system is different to the second data acquisition system, wherein at least one action instruction comprises an audio challenge and a motion challenge, wherein the audio challenge comprises an instruction to say at least one word, and wherein the motion challenge comprises an instruction to perform at least one motion, wherein the at least one motion comprises a head motion, wherein the step of processing the response data comprises processing video data to assess the classification score of at least one characteristic motion associated with the action instruction, wherein processing video data comprises performing facial action recognition on the video data, and wherein performing facial action recognition on the video data comprises: performing a plurality of head pose estimations on the video data; processing the plurality of head pose estimations to form extracted pose information; and forming a facial action classification score using the extracted pose information. performing a plurality of head pose estimations on the video data; processing the plurality of head pose estimations to form extracted pose information; and forming a facial action classification score using the extracted pose information.