A method for operating a display device according to an embodiment includes acquiring an image of a plurality of users, recognizing a plurality of faces respectively corresponding to the plurality of users from the acquired image, checking a viewing state of media content for each user, when the plurality of users respectively corresponding to the plurality of recognized faces are registered users, acquiring viewing information corresponding to at least one of the plurality of registered users of which the viewing state has been changed from a viewing maintaining state in which the media content is viewed to a not-viewing state in which the media content is not viewed, and performing a re-viewing function on the basis of the acquired viewing information when a face of the user of which the viewing state has been changed is re-recognized.