GREYSCALE IMAGE AUTHENTICATION AND REPAIRING

Abstract

It is very necessary to design effective methods to solve image authentication problem, particularly f or images whose security must be protected. In digital documents it is necessary to provide data authentication and repairing of tamper ed data e.g. important documents such as certificates, scanned cheques, drawings, circuit diagrams, signed documents, desig n draft etc. In this paper, a technique for authentication of images with self-re pair capability for fixing tampered image data is eThe input image is assumed to be a binary-type greyscale image with 2 main gray values. Alpha channel is combined in the greyscale image .Using the binary image, authentication signal is calculated w hich is then embedded in the alpha channel to creat e an authentic image. After embedding the authentication signal, image is encry pted. If still Content modifications of the stego-image is detected, then data is repaired at the pixel level using reverse secrete s haring scheme. In case if the alpha channel is com pletely removed from the stegoimage, the integral resulting image is regarded as unauthentic, meaning that the integrity check of th e image fails. The proposed method is based on the generation of (k, n)-thresho ld secret sharing scheme proposed by Shamir. In thi s method a secret message is converted into n shares which is used as authentica tion signal for keeping by n participants; and when k of the n shares are collected, the secret image can be recovered without any loss[ 8]. This type of secret sharing scheme is helpful fthe risk of incidental partial data loss.