Watermarking polygonal lines using Fourier descriptors

Digital products are easy to copy, reproduce, and maliciously process in a network environment. Over the past decade, watermarking has emerged as an important technology for protecting copyright of multimedia products. We present a method for embedding and detecting watermarks in vector graphics images containing polygonal lines, and present results from simulated attacks. Our proposed algorithm embeds watermarks in polygonal lines describing image contours. These contours are usually described in vector format. Our watermarking method slightly modifies the vertex coordinates of the polygonal line. We embed the watermark in the magnitude of the curve´s Fourier descriptors to exploit its location, scale, and rotation invariant properties. Our technique has certain similarities to bitmap image watermarking in the discrete Fourier transform (DFT) domain. However, it´s essentially different because it can be applied to vector rather than bitmap images. Furthermore, Fourier descriptor watermarking problems differ from DFT bitmap image watermarking problems.