the adage “ photos don &# 39 ; t lie ” is no longer reliable . the advent of digital editing tools makes it relatively easy to move , add , or delete features from photographs . other digital content is similarly susceptible to alteration . this problem is at least partially overcome by providing a photograph with supplemental data . this supplemental data is below a threshold of human perception yet can extend throughout the image . if a version of the image is thereafter encountered with the supplemental data missing or attenuated , the image is known to have been altered . by reference to such supplemental data , it is often possible to identify particular regions within the image that have been altered .