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A SEMI FRAGILE CONTENT BASED IMAGE WATERMARKING FOR AUTHENTICATION IN SPATIAL DOMAIN USING DISCRETE COSINE TRANSFORM

A new semi fragile method for embedding watermark data into gray scale images has been proposed. In the proposed scheme, the cover image is partitioned into non-overlapping blocks of size 8 x 8 pixels. The discrete cosine transform of each block is computed. Each block is scaled and a quantization function is used to construct the watermark bit from each block. The image is reconstructed by computing the inverse cosine transform. The gray threshold value of the image in spatial domain is computed. The watermark is embedded to all pixels whose pixel intensity is less than the gray threshold. The proposed scheme has been designed as public watermarking; it does not require the original image to verify its integrity. Experimental results prove the efficiency of the scheme. The proposed scheme can be used to authenticate digital documents of high significance.



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