The main requirements of efficient steganographic systems are transparency, robustness and security. In this work, the proposed system is designed to achieve these requirements, as follows: to increase the transparency and robustness, the proposed system uses the transform domain technique, in this case the wavelet domain technique to embed the color secret image into the color cover image. To achieve high security, chaotic systems are used to accomplish the following two purposes: firstly to scramble the secret color image before hiding it into the color cover image, secondly to randomly select the embedding positions in the cover image. Three chaotic systems with many combinations are used for the scrambling and the embedding process. Experimental results including Mean Square Error (MSE), Peak Signal to Noise Ratio (PSNR), Correlation, Signal to Noise Ratio (SNR) and embedding capacity demonstrate that the proposed system has good performance as compared with other existing methods without attack and under different types of attacks such as filtering and noise attacks. Simulation results show that the combination of chaotic systems providing the best performance include the use of Logistic and Henon maps for the embedding process and Arnold's cat map for the encryption process. The MSE, PSNR, correlation, SNR and embedding capacity obtained in this case reach up to 0.0010, 78.1dB, 0.9999, 67.2dB and 0.39% respectively when the secret image is Airplane with 32×32 pixels and the cover image is Girl with 512×512 pixels. For the extracted secret image, the chaotic system set that provides the best performance includes the use of Arnold's cat map for the encryption process. The MSE, PSNR, correlation and SNR obtained in this case reach up to 0.0846, 58.9dB, 1 and 56.1dB respectively. As compared with other methods, the proposed method achieves gains without any attack of 8.2dB for the stego image and 32.4dB for the extracted secret image in PSNR when the secret image is Airplane with 256×256 pixels and the cover image is Girl with 512×512 pixels.

Wavelet based image steganographic system using chaotic signals

Unlike encryption, steganography hides the very existence of secret information rather than hiding its meaning only. Image based steganography is the most common system used since digital images are widely used over the Internet and Web. The main aim of steganography is to increase the steganographic capacity and enhance the imperceptibility or undetectability. However, steganographic capacity and imperceptibility are at odds with each other. In addition, there is a tradeoff between both steganographic capacity and stego image quality. Hiding more data in cover images (higher capacity) introduces more artefacts into cover images and then increases the perceptibility of hidden data . Furthermore, it is not possible to simultaneously maximize the security and capacity of a steganographic system. Therefore, increasing steganographic capacity and enhancing stego image quality are still challenges. Secret image extraction is done by the proposed technique in which first the cover image is recovered by noise removal methods and then applying alpha blending. Since peak signal-to- noise ratio (PSNR) is extensively used as a quality measure of stego images, the reliability of PSNR for stego images is also evaluated in the work described in this dissertation. The proposed work is compared with the existing method using PSNR, MSE, NCC, MAD, SC as comparison parameters. Proposed technique reduces the requirement to keep record of cover images for secret information extraction. Otherwise for each information received, the receiver should also have the cover image saved with him. In the proposed technique I have tried to obtain the secret image from stego image without having cover image, considering secret image as noise. The technique deals with steganography in wavelet domain. Complete work can be seen as adding noise to cover image, and then using noise removal technique to obtain secret image. Soft thresholding and bilateral filtering used for removing noise are efficient. Experimental results shows that there's a trade - off between stego image and secret image extracted. It is seen that as we increase the value of alpha, stego image degrades, but secret image improves. The secret image obtained is in visually acceptable form. Results shown are objective and subjective in nature.

Manisha Boora

Papers

Binary Text-Image Steganography