Authentication of binary document images in PNG format based on a secret sharing technique

A new authentication method utilizing the secret sharing technique to resist attacks with a data recovery capability for binary document images in PNG format is proposed. An authentication signal is generated for each block of a cover image, which together with the block content is transformed into several shares using the Shamir secret sharing scheme. The shares then are embedded into the alpha channel plane of the input PNG image in a carefully designed manner. In the process of image authentication, an image block is marked as tampered if the authentication signal computed from the current block content does not match that extracted from the shares embedded in the alpha channel plane. Data recovery is conducted for each tampered block by a reverse Shamir scheme after collecting enough shares from unmarked blocks. Experimental results prove the effectiveness of the proposed method for real applications.