Abstract

Digital Steganography exploits the use of a host data to hide a piece of information in such away that it is imperceptible to a human observer. Wavelet transforms that map integers to integers allow perfect reconstruction of the original image. Hence, we proposed an algorithm that embeds the message bitstream into the LSB's of the integer wavelet coefficients of a true-color image. The algorithm also applies a preprocessing step on the cover image to adjust saturated pixel components in order to recover the embedded message without lose. Experimental results showed the high invisibility of the proposed model even with large message size.

Introduction

The appearance of the Internet is considered to be one of the major events of the past years; information become available on-line, all users who have a computer can easily connect to the Internet and search for the information they want to find. This increasing dependency on digital media has created a strong need to create new techniques for protecting these materials from illegal usage. One of those techniques that have been in practical use for a very long time is Encryption. The basic service that cryptography offers is the ability of transmitting information between persons in a way that prevents a third party from reading it.

Although, encryption protects content during the transmission of the data from the sender to receiver, after receipt and subsequent decryption, the data is no longer protected and is in the clear. That what makes steganography compliments encryption. Digital Steganography exploits the use of a host (container) data to hide or embed a piece of information that is hidden directly in media content, in such a way that it is imperceptible to a human observer, but easily detected by a computer.

The principal advantage of this is that the content is inseparable from the hidden message. In a blind image steganographic system, a message is embedded in a digital image by the stegosystem encoder which uses a key. The resulting stego-image is transmitted over a channel to the receiver where it is processed by the stegosystem decoder using the same key. In general, if the channel is monitored by someone who is allowed to modify the information flow between the two parties, he is called an active warden; but if he can only observe it, he is called a passive warden.

The scientific study of steganography began in 1983 when Simmons stated the prisoner's problem. During the past few years, there has been a lot of research on developing techniques for the purpose of placing data in still images. Some techniques are more suited to dealing with small amounts of data, while others to large amounts. Some techniques are highly resistant to geometric modifications, while others are more resistant to non-geometric modifications, e.g., filtering. Current methods for the embedding of messages into cover images fall into two main categories: High bit-rate data hiding and low bit-rate data hiding, where bit-rate means the amount of data that can be embedded as a portion of the size of the cover image. In this section, we will survey methods that explore both of these areas. In low bit-rate encoding, we expect a high level of robustness in return for low bandwidth. 

Conclusions

Wavelet transforms that map integers to integers allow perfect reconstruction of the original image. The proposed algorithm deals with true-color images and applies the S-Transform on each color plane separately. The embedding process stores up to 4 message its in each integer coefficient for all the transform sub-bands. The algorithm readjusts the original cover image in order to guarantee that the reconstructed pixels from the embedded coefficients would not exceed its maximum value and hence the message will be correctly recovered. The information capacity provided by the proposed algorithm can reach 50% of the original cover image size. Furthermore, experimental results showed that this scheme retains high quality of the stego-image over the existing LSB-based methods.