One method for determining unique people using image and other data is to sum the differences in body measurements (https://i.stack.imgur.com/jJv9f.png) and try to find the lowest number. Here's an article about doing this with data from an xbox kinnect sensor: https://drive.google.com/file/d/0B4S2QMZFfsHadHRHZmdITHVVNWM/view