A method includes receiving a first image and a second image, wherein the first and second images represent first and second relative locations, respectively, of an image acquisition device with respect to a subject. The method also includes determining, using the first and second images, a total relative displacement of the subject with respect to the image acquisition device between a time of capture of the first image and a time of capture of the second image, and determining, based on sensor data associated with one or more sensors associated with the image acquisition device, a component of the total relative displacement associated with a motion of the image acquisition device. The method also includes determining, based on a difference between the first total relative displacement and the component, that the first subject is an alternative representation of a live person, and in response, preventing access to a secure system.