A Visual Cryptographic Scheme To Secure Image Shares Using Digital Watermarking

Visual Cryptographic Scheme is a special technique used to send the data securely over the network. It is a technique which allows visual information (pictures etc.) to be encrypted in such a way that the decryption can be performed by the human, without using any decryption algorithm or without doing any computation. In this paper we have introduced the new technique known as the “Digital Watermarking” technique in order to secure or ensure the owner authentication. Digital Watermarking is almost same as that of the Steganography but as steganography more focused about hiding the information over a cover object so that it cannot be perceived by the user but in watermarking the hidden information is usually related to the cover image. In this we have introduced the new technique, digital watermarking as the simple visual cryptography is not so secure for sharing of data and it also does not ensure the owner authentication. This cryptographic technique involves dividing the secret image into n shares and a certain number of shares (m) are sent over the network. A distinctive property of VCS is that one can visually decode the secret image by superimposing shares without computation. The project presents an approach for embedding visual cryptographically generated image shares in the host images to provide authentication for the VC shares and makes these secret shares invisible by embedding them into host images. The share is embedded into the host image in Frequency Domain using Discrete Cosine Transform (DCT). In frequency domain, the obtained marked image must be less distorted when compared to the original image. Earlier it was implemented in spatial domain but it was not successful as the marked image was very much distorted and not able to bear the attacks. In this paper we have discussed about the watermarking, how it can be done and upto which level it can bear the attacks. OVERVIEW Visual Cryptography is a special encryption technique to hide information in images in such a way that it can be decrypted by the human vision if the correct key image is used. The technique was proposed by Naor and Shamir in 1994 [1]. It is used for the secure encryption of the visual information like written notes, videos etc. in a secure way so that decryption becomes a mechanical operation that does not require computer it means that decryption can be done using the human visual system i.e. human eye. Visual Cryptography (VC) [2] is a method of encrypting a Secret image into shares such that stacking a sufficient number of shares reveals the secret image. It is a visual secret sharing scheme, where an image was broken into n shares so that only someone with all n shares could decrypt the image, while any n − 1 shares revealed no information about the original image. Each share was printed on a separate transparency, and decryption was performed by overlaying the shares. When all n shares were overlaid, the original image would appear. It is shown in Fig 1(a) & Fig 1(b) Fig 1(a): Two shares of a Secret image Fig 1(b): Embedded image Occurs. Watermarking is the technique of embedding a secret image into a cover image without affecting its perceptual quality so that secret image can be revealed by some process. One significant advantage of watermarking is the inseparability of the watermark (secret image) from the cover image. A watermark technique has few characteristics like ‘robust’ with respect to transformations if the embedded information may be detected reliably from the marked image, even if degraded by any number of transformations. Typical image degradations are JPEG compression, rotation, cropping and additive noise. Share generation in visual cryptography can also be done using the watermarking technique. We can use these watermarked shares to retrieve the hidden information. Watermarking techniques can be categorized into different types based on a number of ways. Watermarking can be divided into Non-blind, Semi-Blind and Blind schemes based on the requirements for watermark extraction or detection. Non-blind watermarking schemes necessitate the original image and secret keys for watermark detection. The Semi-Blind schemes require the secret key(s) and the watermark bit sequence for extraction, whereas, the Blind schemes need only the secret key(s) for extraction. Digital watermark is a visible or perfectly invisible, identification code that is permanently embedded in the data and remains present within the data after any decryption process. It means with visible watermarking of images, a secondary image (the watermark) is embedded in ISSN:0975-9646 Malvika Gupta et al, / (IJCSIT) International Journal of Computer Science and Information Technologies, Vol. 6 (5) , 2015, 4339-4343