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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 \leq t \leq n tagged visual cryptography (TVC) scheme works like a traditional VC scheme does, where the original image is encoded in n shares in such a way that the secret can be revealed by superimposing any t or more shares, but knowledge of less than t shares 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. [ABSTRACT FROM PUBLISHER]

Abstract: Visual cryptography (VC) is an image-based secret protection mechanism in which the decoding process is conducted by inspecting the stacked shares with the unaided eye. In traditional VC schemes, the content of an image is usually processed as a single secret, which limits the whole image to unique secret property. Recently, Wang ( IEEE SPL, 16(2009) 659–663) proposed an n-level region incrementing VC scheme which has the ability of incremental revealing of the secrets on an image; however, the pixel expansion of the generated shares increases rapidly in the proposed scheme as n grows. In this paper, we propose an incrementing VC scheme using random grids. The method has the same incremental revealing effect to the secrets on an image, and the size of each share is the same as that of the original image without any expansion. The smaller size of shares makes their further processing such as storage and/or printing out more efficient. [ABSTRACT FROM AUTHOR]