Digital Watermark Research In Vector Graphic And Image

As the development of digital multimedia technology, it has emerged a hot point on research to protect copyrights of digital multimedia works against piracy and to distinguish between genuine and fake. In this dissertation, we study the technologies of digital image watermarking in watermark verifying process and 2D vector polygonal graphics watermarking. The main contributions of this dissertation are as following:(1) Circle-based Digital Watermarking Algorithm for Closed Polygonal CurvesThe polygonal curves (closed or non-closed) often appear in contour maps, in which many lines concatenate together. In our algorithm, we expand the original closed curve into a circle at first keeping the circumference the same as the length of the curve, which equals to the summary of all the polygonal lines. At the same time, those vertexes of the lines on the curve are mapped onto the circle, keeping the arc length between each two adjacent vertexes the same the length of the corresponding line. Then the digital watermarking data array can be embedded into the arc angles corresponding to each arcs on the circle. After that, those vertexes are mapped backwards into the watermarked curve. For contour map, some distortion (not too much) caused by watermarking is tolerable. Otherwise it will become useless. Since the limitation of circumference, we can control the amount of distortion within tolerable scope. This algorithm is robust against graphical geometrical transformation, while not fit for large distortion application.(2) B Spline-based Digital Watermarking Algorithm for Parameter CurveAs the situation in image watermarking algorithm, it is worthy to research how to embed watermarking into transform field of a curve. Unfortunately, we don't have such mathematic theoretical method (like DCT/DWT) to transform a curve. Therefore, we focus on parameter curve theoretical method, by which we can embed the watermark data array into parameter data of the curve. Then it is transformed backwards to get the watermarked curve. This algorithm is robust against geometrical transform, also some vertex-attacking method. If the iterative algorithm (in (3)) is applied in the watermark detecting process, this embedding algorithm can resist vertex attacking.(3) The Iteration Algorithm to Retrieve The CurveThere are many watermark embedding algorithm in literature, which can resist common geometrical transform, such as translate, rotate, scale, and map. But they are not robust against vertex attacking methods, especially after resampling or re-vectorizing the curve. Since those methods are based on coordinates of vertexes on the curve, they can't resist vertexes attacking which changes the coordinates or the relative position among vertexes. In the iteration algorithm, we can retrieve the original parameter points to detect watermarking data, even after re-sampling or re-vectorizing the curve. This algorithm makes our embedding algorithm be able to against re-sampling or re-vectorizing attacking methods, so that the watermark data is survived.(4) Zero-knowledge-based Secure Watermark Verifying SchemeFrom the watermark attack methods, we find that the unsafe verifying process can introduce great risk to original digital works, even we do well in watermark embedding and retrieving processes. We proposed a secure scheme to verify watermark existence and prove the ownership or copyright of a multimedia work based on zero-knowledge protocol. The proving process, which follows zero-knowledge protocol, should be successful if the prover is true, otherwise, it would be failure. Whatever the process is successful or failure, the verifier can not get new knowledge concerning the multimedia work to be proved from the whole proving process. Thus it keeps the multimedia work or the original digital data safe during the whole watermark verifying process. What the verifier only can do is to accept the declaration of ownership or copyright, or reject it.