Authentication of Gray Scale Document Images via the Use of PNG Image with Data Repairing

A new authentication method based on the secret sharing technique along with a data repairing capability for gray scale document images via the use of PNG (portable network graphics) is proposed. An authentication signal is generated for every and each block of a gray-scale document image, which, in conjunction with the binarized block content, is remodeled into many shares exploitation the Shamir secret sharing theme. The concerned parameters are cautiously chosen in order that as several shares as potential are generated and embedded into an alpha channel plane. To form a PNG image the alpha channel plane is combined with the original gray scale image. During the embedding process, the computed share values are mapped into a range of alpha channel values near their maximum value of 255 to yield a transparent stego-image with a disguise effect. While the method of image authentication, an image block is spotted as tampered, if the authentication signal computed from the present block content doesn't match with the worth or value extracted from the shares embedded inside the alpha channel plane. For each tampered block, data repairing is applied by using reverse Shamir scheme after collecting two shares from unmarked blocks. Some security measures for protecting the security of the data hidden in the alpha channel are also proposed. For real time applications, good experimental results prove the effectiveness of the proposed method.