Steganographic Techniques For Digital Images

Steganography, meaning hidden writing, is the technique of concealing secret information into another cover-media, such as audio, video, image and text, in such a manner that the very existence of the information is camouflaged. Unlike the goal of cryptography, which prevents the data from illicit access and modification by transforming the secret data into messy and meaningless bit-streams, the aim of steganography is to conceal their very existence such that the embedded data is inaudible or invisible to the grabbers. Using cryptographic techniques, the transformed secret bit-streams may draw the eavesdroppers'attention, while using steganographic techniques, the interceptors may not notice the existence of the hidden data.In this research work, steganographic techniques for digital images, which are used as a cover-media, are investigated arid analyzed and two data hiding techniques are proposed so that the hiding capacity can be maximized without incurring perceptible degradation in the image quality and the embedded secret data can be recovered correctly without referencing the original cover-image.In the proposed Pixel value difference technique, the side information of neighboring pixels is used to estimate the number of bits which can be carried in the pixel of the cover-image. The pixel value is then replaced by the new value which includes the secret data. In the proposed method, the pixel value difference between upper, lower, left and right neighboring pixel of the input pixel is used to determine the amount of data can be inserted into the pixel. More secret bits are embedded in the edge area than those in the smooth area as the change in smooth area is more easily discovered by human eyes. Besides, the embedded secret data can be extracted completely from the resulting stego-image without any errors. The proposed technique provides a relatively high hiding capacity and relatively good quality stego-image. In the second proposed technique i.e. DWT-DCT based steganography; a data hiding methods for transmitting the important data securely has been described. In these methods, text data can be embedded into the cover-image. Jian Zhao and Eckhard Koch proposed an image hiding Method which is the process is similar to the spread-spectrum approach first utilized first in World War II. The proposed method attempts to hide the secret message (text) by manipulating HL, LH and HH sub band frequency domain coefficients. Modifications have been made to the existing process in order to increase the size of secret message.