| Summary: | 碩士 === 國立高雄第一科技大學 === 電腦與通訊工程系碩士班 === 105 === With the progress of technology, digital multimedia has been applied extensively throughout society. Because the transmission and exchange of information is comparatively easy, pirating and misuse problems have also gradually risen, so determining how to prevent digital images from illegal tampering has also become an important issue. Watermarking technology embeds copyright information or a verification signal in the carrier. In general, regarding watermark technologies, when watermarks are removed from the carrier, the original carrier content cannot be fully restored. In this paper, we propose a semi-fragile lossless watermarking method for digital images. The method first carries out the two-level Integer Wavelet Transform on the image, and calculates the verification signals which represent the image’s features from the coefficients of the high frequency region. The verification signals and restored information are embedded in the less important middle frequency and high frequency coefficients after the one-level Integer Wavelet Transform. The method does not change the important low frequency coefficients in order to maintain image quality. During the time of embedding, the embedding positions of the verification signals are selected by a random number to avoid the occurrence of regular distortion. In the process of image verification, the extracted verification signals are compared to the signals calculated from the image. Erosion and dilation operations are used to enhance the accuracy of image verification. This method can restore the original image from the extracted ‘restore information’ without any distortions. The experimental results show that the proposed method can effectively resist attacks of general image operations which do not change image contents, and can correctly point out the tampered areas resulting from the malicious tampering which modified the content of the images.
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