Protecting publicly-available images with an invisible image watermark

Abstract

A method is presented for marking high-quality digital images with a robust and invisible watermark. A broad definition of robustness, stated as fundamental, is used. It requires the invisible mark to survive and remain detectable through all image manipulations that in themselves does not damage the image beyond useability. These manipulations include JPEG `lossy' compression and, in the extreme, the printing and rescanning of the image. The watermark is imparted onto an image as a random, but reproducible, small modulation of its pixel brightnesses, and becomes a permanent part of the marked image. Detecting the imparted watermark, especially after image manipulation, is a daunting task. It is one of detecting the presence of a known small modulation of a random carrier, where the carrier is composed of the pixel brightness values of the unmarked image. The method presented exploits the not well understood but superb ability of the human visual system to recognize a correlated pattern in a scatter diagram called a `visualizer-coincidence image.' Results of application of the method are presented.