C.-C. Ko and C.-H. Huang (Taiwan)
Digital Watermarking, Image Authentication, Copyright Protection, Pre-quantization, Distortioncompensation.
In this paper, we proposed an image authenticating system based on the semi-fragile watermarking technique. Firstly, a discrete Cosine transform (DCT) was performed to transform image date from spatial domain into frequency domain. Secondly, DCT coefficients were quantized in order to reduce variance resulting from quantization and enhance the efficiency of detection if image data were maliciously attacked. Lossy compensation was then performed to resist reasonable geometric distortion, reduce the visibility of the embedded image, and increase the image quality after DCT coefficients were embedded into the watermark. Finally, we analyzed the extracted watermarks, and determined malicious tampering or acceptable distortion in the embedded image. Experimental results show that our proposed method may detect the tampered areas after reasonable image processing and malicious attacks. Moreover, the proposed method can also obtain high image quality for image processing using acceptable JPEG lossy compression.
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