IMAGE STEGANOGRAPHY USING BLOCK DIFFERENCES

Abstract

Steganography is a means to hide the existence of information exchange. Using this technique the sender embeds the secret information in some other media. This is done by replacing useless data in ordinary computer files with some other invisible information. The hidden information could be simple text, cipher text or even images. The media used as the embedding plane could be an image, audio, video or a text files. Using steganography ensures that no one apart from the sender and the receiver knows about the existence of the message. In this thesis, a steganography method based on block differences is used. Each block consists of three pixels. Two different differences are calculated for each block – between the first and the second pixel and also between the second and the third pixel. The most recurring absolute block difference in the whole image is used for embedding the secret message. To embed bit “1” or “0”., the selected difference is either increased or left unchanged respectively. At the most a single block can embed two bits “11” and only the middle pixel needs to be changed. Data Compression is used to reduce the size of information so that the data hiding capacity of the images could be increased. The major advantage of using this technique is that the image quality is not degraded even if the number of embedded characters is increased. The algorithm operates above 50 db in most of the test cases. The average payload capacity is also considerably high