The adage "photos don't lie" is no longer reliable. The advent of digital editing tools makes it relatively easy to move, add, or delete features from photographs. Audio content is similarly susceptible to alteration. This problem is at least partially overcome by providing the content with supplemental data that is below a threshold of human perception. If a version of the content is thereafter encountered with the supplemental data missing or attenuated, it is known to have been altered. By reference to such supplemental data, it is often possible to identify particular portions of the content that have been altered.