An authentication method for grayscale document images, based on the secret sharing technique with a data repair capability via the use of Portable Network graphics (PNG) image is proposed. An authentication signal is generated for each block of a grayscale document image and then using Shamir secret sharing scheme grayscale document image authentication signal and binarized block content is combined and transformed into several shares. These several binarized block content shares are combined into an alpha channel plane. The original grayscale image combines with alpha channel plane to form a PNG image. If the authentication signal measured from the current block content does not match that extracted from the shares embedded in the alpha channel plane then image block is marked as tempered. Further, two shares from unmarked blocks are collected using reverse Shamir scheme and then data repairing is applied. Some security measures for protecting the security of the data hidden in the alpha channel are also proposed.

1. C. S. Lu and H. Y. M. Liao, oct. 2001 multipurpose watermarking for image authentication and protection, IEEE Trans. Image Process. , vol. 10, pp. 1579-1592.
2. Shamir, Nov. 1979How to share a secret,Commun. ACM, vol. 22, no. 11, pp. 612–613.
3. H. Tzeng and W. H. Tsai, Nov. 1979A new approach to authentication of binary images for multimedia communication with distortion reduction and security enhancement,IEEE Commun. Lett. , vol. 7, no. 9, pp. 443–445.
4. H. Yang and A. C. Kot, Dec. 2006Binary image authentication with tampering localization by embedding cryptographic signature and block identifier,IEEE Signal Process. Lett. , vol. 13, no. 12, pp. 741–744.
5. M. Wu and B. Liu, Aug. 2004Data hiding in binary images for authentication and annotation,IEEE Trans. Multimedia, vol. 6, no. 4, pp. 528–538.
6. R. B. Wolfgang and E. J. Delp, "Fragile watermarking using the VW2D watermark", inSecurity and Watermarking of Multimedia content, VOL. 3657of SPIE proceedings, January 1999.
7. Fridrich J (1998b) Methods for tamper detecting in digital images. In: Proceedings of the 6th IEEE international workshop on intelligent signal processing and communication systems (ISPACS '98), Melbourne, Australia
8. C. Y. Lin and S. F. Chang, "Semi-fragile watermarking for authenticating JPEG visual content", in Proc. SPIE International Conf. On Security and Watermarking of Multimedia Contents, VOL. 3971, January 2000.
9. Che-Wei Lee, Student Member, IEEE, and Wen-Hsiang Tsai, "A Secret-Sharing-Based Method for Authentication of Grayscale Document Images via the Use of the PNG Image With a Data Repair Capability", IEEE transaction on image processing, VOL. 21, NO. 1, JAN 2012.
10. Venkatesan R, Koon S, Jakubowski M (2000) Robust image hashing. In: Proceedings of the IEEE international conference on image processing, vol 3, pp 664–666

Data repair grayscale document image image authentication PNG secret sharing.