Embedding of Metadata and Authentication of an Image via the use of PNG Image with Data Integrity

Digital image is a form of preserving important information. Using the advance of digital technologies it is easy to make visually imperceptible modifications to the content of digital images. To ensure the integrity and the authenticity of a digital image is very difficult. A new authentication method based on the secret sharing technique with data integrity for grayscale document images via the use of the portable network graphics (PNG) image. An authentication signal is generated for each block of a grayscale document image which together with the binarized block content is transformed into several shares using the Shamir secret sharing scheme. The shares are embedded into an alpha channel plane. The alpha channel is combined with the original grayscale image to form a PNG image. During the embedding process, the computed share values are mapped into range of alpha channel values near their maximum value of 255 to yield a transparent stego image with a disguise effect. In the process of image authentication, image block is marked as tampered if the authentication signal computed the alpha channel plane. The tampered block can be rectified by collecting two shares from unmarked block and apply reverse Shamir secret scheme. With this method the authentication of grayscale document image is effective without the change of the original image.