Data hiding for text document image authentication by connectivity-preserving

In this paper, a novel blind data hiding method for text document images aims to preserve the connectivity in a local neighborhood is proposed. The "flippability" of a pixel is determined by imposing the three transition criterions in a 3 x 3 moving window which is centered at the pixel. The "embeddability" of a block is invariant in the watermark embedding process. While the "flipped" pixels can be located by imposing a constraint. The "uneven embeddability" of the host image is considered by embedding the watermark only in those "embeddable" blocks. The location is chosen in such a way that the visual quality of the watermarked image is guaranteed. Different types of blocks are employed and their abilities to increase the capacity are compared. A hard authenticator watermark is also generated to ensure the integrity and authenticity of the document.