Spatially varying gray component replacement for image watermarking

We present a method to include watermarks in printed images. We spatially vary the GCR along the image in a manner that is not perceptible, and we employ an estimation method to detect such changes. The choice of GCR for a given pixel (or region) comprises an additional information channel that embeds a watermark or hidden information. For that, we estimate the RGB values of each pixel and the CMYK values on the paper by scanning the printed page. With that information, we can estimate which GCR strategy was used in a given region and retrieve the watermark message. We are only concerned with robustly estimating the GCR strategy. Promising results illustrate the method´s potential to watermark printed images.