Embedding invisible information in color images

We describe a method for embedding information in color images. A model of human color vision is used to ensure that the embedded signal is invisible. Sinusoidal signals are embedded so that they can be detected (decoded) without use of the original image. The sinusoids act as a grid, providing a coordinate frame on the image. We use the grid to automatically scale and align (deskew) images that have been printed and then scanned.