Hyung-Shin Kim Korea Advanced Institute of Science and Technology (South Korea) Yunju Baek Ansung National Univ. (South Korea) Heung-Kyu Lee Korea Advanced Institute of Science and Technology (South Korea)
Digital watermarks offer means of protecting the copyright of digital multimedia. However, many of the proposed watermarking methods are vulnerable to the geometrical distortions that occur during normal use of the media. We propose a new image watermarking method that is resilient to rotation, scaling, and translation (RST). We use the higher order spectra (HOS), in particular, the bispectrum feature vector of an image as the watermark. The bispectrum is the Fourier spectrum of the triple correlation of a signal. Phases of the integrated bispectra are invariant to translation and scaling. Rotation invariance is achieved using the Radon transform of the image. An image is decomposed into the 1-D projections and we construct a feature vector from them. A watermark is embedded by modifying the vector. We measure the distance between the feature vector extracted from the test image and the watermark at detector. Results of experimental studies show that our method is robust to geometric attacks, JPEG compression, and Gaussian noise.