Yeuan-Kuen Lee

Sharing multiple secrets in visual cryptography

The secret sharing schemes in conventional visual cryptography are characterized by encoding one shared secret into a set of random transparencies which reveal the secret to the human visual system when they are superimposed. In this paper, we propose a visual secret sharing scheme that encodes a set of x≥2 secrets into two circle shares such that none of any single share leaks the secrets and the x secrets can be obtained one by one by stacking the first share and the rotated second shares with x different rotation angles. This is the first true result that discusses the sharing ability in visual cryptography up to any general number of multiple secrets in two circle shares.

An efficient segmentation algorithm for CAPTCHAs with line cluttering and character warping

A CAPTCHA is a test designed to distinguish computer programs from human beings, in order to prevent the abuse of networked resources. Academic research into CAPTCHAs includes designing friendly and secure CAPTCHA systems and defeating existing CAPTCHA systems. Traditionally, defeating a CAPTCHA test requires two procedures: segmentation and recognition. Recent research shows that the problem of segmentation is much harder than recognition. In this paper, two new segmentation techniques called projection and middle-axis point separation are proposed for CAPTCHAs with line cluttering and character warping. Experimental results show the proposed techniques can achieve segmentation rates of about 75%.

An Advanced Least-Significant-Bit Embedding Scheme for Steganographic Encoding

The advantages of Least-Significant-Bit (LSB) steganographic data embedding are that it is simple to understand, easy to implement, and it results in stego-images that contain hidden data yet appear to be of high visual fidelity. However, it can be shown that under certain conditions, LSB embedding is not secure at all. The fatal drawback of LSB embedding is the existence of detectable artifacts in the form of pairs of values (PoVs). The goals of this paper are to present a theoretic analysis of PoVs and to propose an advanced LSB embedding scheme that possesses the advantages of LSB embedding suggested above, but which also provides an additional level of communication security. The proposed scheme breaks the regular pattern of PoVs in the histogram domain, increasing the difficulty of steganalysis and thereby raising the level of security. The experimental results show that both the Chi-square index and RS index are less than 0.1, i.e., the hidden message is undetectable by the well-known Chi-square and RS steganalysis attacks.

A Method for Automatic Identification of Signatures of Steganography Software

A fully automated, blind, media-type agnostic approach to steganalysis is presented here. Steganography may sometimes be exposed by detecting automatically characterized regularities in output media caused by weak implementations of steganography algorithms. Fast and accurate detection of steganography is demonstrated experimentally here across a range of media types and a variety of steganography approaches.

A Vision-Based Augmented-Reality System For Multiuser Collaborative Environments

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 cameras 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.

Verifiable Visual Cryptography

The paper presents a verifiable visual cryptography (VC) scheme for checking the validness to the shares engaged in a VC decoding instance. The idea is to stamp a continuous pattern on the shares belonging to the same secret image, and a part of the pattern can be revealed through aligning and stacking half of two shares together. The visual coherent among the revealed patterns of all pair of shares provides evidence to the genuine of the shares engaged in the decoding process. Compare to the reported cheating prevention VC schemes, the proposed scheme maintains the original pixel expansion in VC scheme without cheating prevention ability, and the share verification process is done without resorting to any additional verification image. Besides, the proposed verification mechanism can easily be attached to any VC schemes in the literature to endow legitimate user with the ability to prevent cheating from malicious participants.

A Novel Data Hiding Method Using Sphere Encoding

In this paper a novel data hiding scheme using least square mapping is proposed. The method conceals a k-ary secret digit in n-pixel block in which the embedding function with minimum mean square error (MSE) between the cover block and the stego-block is searched. The constructions for the proposed method in three-pixel block (sphere encoding) under different k are demonstrated. Experiment results show that the proposed scheme achieves higher embedding efficiency than several reported steganographic schemes.

Multisecret Image Sharing

This paper proposes a multisecret image sharing (MSIS) scheme for sharing multiple secrets in an image among n participants. In the proposed n-level MSIS scheme, the content of an image S is designated to multiple regions associate with n levels of secrets, and encoded to n+1 shadow images which exhibit the following features: (a) each shadow image cannot get any region in S, (b) any t (2

Threshold-based successive elimination algorithm for block motion estimation

The successive elimination algorithm (SEA) has already proved successful in block motion estimation. This paper presents a simple and efficient algorithm called the threshold-based SEA as a search engine to take advantage of the simplicity of the SEA while avoiding its redundant computation. In addition, the threshold-based SEA utilizes a threshold adaptation mechanism to efficiently distribute the available computational power of the employed codec to blocks of video sequences. Since the threshold-based approach is performed at each search candidate block, it can be combined not only with the SEA but also with other fast algorithms, including the three-step search, the block-based gradient descent search, and the diamond search. Depending on the motion activity in the sequences, experimental results indicate that the threshold-based approach can uniformly achieve a quality improvement over the original SEA for the same computation.