User attribute data, such as a retinal scan, is encoded into a media signal as it is captured in media capture device, such as a camera, video recorder, etc. The user attribute data uniquely associates the creator with the content he or she creates. By steganographically embedding the user attribute data into the content at or near the time of capture, the creator of the content can be authenticated at a subsequent time. In addition, alteration of the content can be detected.