The QR code is the most widely used two-dimensional barcode in the world, and it has been successfully applied in many applications in manufacturing and marketing fields. This letter presents a new variant of the QR code named the nested QR code. It comprises two QR codes with individual messages on a shared square image. The two QR codes can be read separately by slightly adjusting the distance and angle at which images are obtained using standard QR code readers. Construction methods for generating the proposed nested QR code with high decoding robustness are presented, and experimental results verify the feasibility of the proposed method.

This letter presents a method for implementing visual cryptography (VC) in which an additional tag is attached to each generated share. The proposed (t,n), 2 ≤t≤ntagged visual cryptography (TVC) scheme works like a traditional VC scheme does, where the original image is encoded innshares in such a way that the secret can be revealed by superimposing anytor more shares, but knowledge of less thantshares gets no secret information. A notable characteristic of TVC is that an extra tag can be revealed by folding up each share, which provides users with supplementary information such as augmented message or distinguishable patterns to identify the shares. The tagging property can easily be applied to any reported VC scheme to endow the generated shares with more capabilities. Construction methods and simulation results of the proposed (t,n) TVC based on conventional matrix-based VC and probabilistic-VC are illustrated in the letter.

In 2007, Wang and Shyu proposed a scalable secret image sharing scheme in which three sharing styles, namely the multisecret, priority, and progressive modes, are designed to encode an image with diverse revealing effects. Their scheme is a (2, n ) sharing method where each generated shadow image is half size of the original image. This letter proposes a general (t,n), 2 ? t ? n, scalable secret image sharing scheme with the same revealing effects. Notably, the size of each generated shadow image is only (2n-t)/n 2 times of the original image. The smaller size of the generated shadow images makes their transmission and storage more efficient.

This letter proposes a steganalysis scheme for detecting reversible contrast mapping (RCM) watermarking. RCM watermarking involves the transformation of pixel pairs belonging to the RCM domain, which introduces artifacts into the least-significant bit (LSB). We found that the LSB histogram varies between a stego-image to the cover image, and we used this information to design a specific steganalysis method for detecting RCM watermarking and also estimating the length of the hidden message. The experimental results show that the proposed scheme successfully breaks RCM watermarking for various embedding rates and can also accurately estimate the message length.

This letter presents a novel visual cryptography scheme, called region incrementing visual cryptography (RIVC), for sharing visual secrets with multiple secrecy levels in a single image. In the proposed n-level RIVC scheme, the content of an image S is designated to multiple regions associated with n secret levels, and encoded to n+1 shares with the following features: (a) each share cannot obtain any of the secrets in S, (b) any t (2lestlesn+1) shares can be used to reveal t-1 levels of secrets, (c) the number and locations of not-yet-revealed secrets are unknown to users, (d) all secrets in S can be disclosed when all of the n+1 shares are available, and (e) the secrets are recognized by visually inspecting correctly stacked shares without computation. The basis matrices for constructing the proposed n-level RIVC with small values of n=2, 3, 4 are introduced, and the results from two experiments are presented.

This paper proposes a method for hiding an important image in a cover image whose size is limited. In this method, in order to save space, a modified search-order coding (MSOC) technique first transforms the important image, then, a randomization procedure permutes the transformed image to further increase the security. Finally, a modulus function embeds the permuted code in a cover image; notably, in the modules function, the modulus base used for a pixel is determined according to the variance of its neighboring pixels. Experimental results show that the images are of high quality. Comparisons with reported methods are provided.

This work presented a novel vision-based augmented-reality system for applications in multiuser collaborative environments. The kernel technology of this vision-based system locates the cameras that are utilized to point and simulate the positions of multiple viewers. Camera calibration based on computer vision is employed during the camera's locating process. The applications in multiuser collaborative environments allow the viewers to view various positions and in numerous directions. However, traditional calibration approaches are not suitable for these cases sufficiently. A novel calibration pattern based on pseudo-random arrays is designed for multiuser collaborative applications. The pattern has a simple and regular structure, easily extracts features, achieves robust recognition using local information, and does not limit viewer positions and directions. Experimental results indicate that the proposed system provides a effective platform for applications in multiuser collaborative environments.

This letter presents a novel image steganography method that utilizes a two-way block-matching procedure to search for the highest similarity block for each block of the important image. The bases and indexes obtained together with some not-well-matched blocks are recorded in the least significant bits of the cover image using a hop scheme. The method exhibits a high data payload, which reduces the storage and transmission-time requirements and also provides a method that prevents an observer from selectively blocking the transmission of the important image.