Fleet DJ & Heeger DJ. Embedding invisible information in color images, in Proceedings of International Conference on Image Processing, 1997.
Abstract: 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 the 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.