A new approach to the secret image sharing with steganography and authentication

Steganography can be viewed as cryptography. It includes a variety of secret communication methods that embed the existence of the message and makes it appear invisible. Both of them have been used to protect secret information. In 2004, Lin and Tsai proposed a novel secret image sharing method that was based on the (k, n)-threshold scheme with the additional capabilities of steganography and authentication. They protect a secret image by breaking it into n user-selected ordinary camouflage images. Besides, their methods also embed fragile watermark signals into the camouflage images by using parity bit checking. Recently, Yang et al. have shown three weaknesses in Lin-Tsai's scheme and further proposed improvements in 2007. They not only improve authentication ability and image quality of stego-image, but also introduce a lossless version image sharing scheme for secret image. Unfortunately, there is a common drawback both in Lin-Tsai's and Yang et al.'s scheme: The enlargement size of the camouflage images and stego-images must be 4 times of the secret image. The proposed scheme does only require 3.5 times enlargement. In addition, the experimental results of image quality analysing show that the proposed scheme has better image quality than previous methods. In other words, the proposed scheme is able to save storage space as well as to improve the image quality.