DWT Based Invisible Watermarking Technique for Digital Images

The two most aspects of any image based steganographic system are the quality of the stego-image & the capacity of the cover image. A lossless data hiding scheme is presented based on quantized coefficients of discrete wavelet transform (DWT) in the frequency domain to embed secret message. Using the quantized DWT based method, we embed secret data into the successive zero coefficients of the medium- high frequency components in each reconstructed block for 3- level 2-D DWT of cover image. The procedures of the proposed system mainly include embedding & extracting. The original image can be recovered losslessly when the secret data had been extracted from stego-image. Information hiding is a technique in the field of information security presently. It hides the existence of important information into cover-object to form stego-object. A cover image is an image file into which a secret message will be embedded. A stego image is an image file which has been altered to contain a message. The Steganography is used for secret data transmission. In steganography the secret image is embedded in the cover image and transmitted in such a way that the existence of information is undetectable. The digital images, videos, sound files and other computer files can be used as carrier to embed the information. The object in which the secret information is hidden is called covert object. Stego image is referred as an image that is obtained by embedding secret image into covert image. The hidden message may be plain text, cipher text or images etc Steganography is a method of hiding secret information using cover images. Audio steganography embeds the message into a cover audio file as noise at a frequency out of human hearing range. One major category, perhaps the most difficult kind of steganography is text steganography or linguistic steganography because due to the lack of redundant information in a text compared to an image or audio. Data hiding methods for images can be categorized into two categories. They are spatial-domain and frequency-domain ones. In the spatial domain, the secret messages are embedded in the image pixels directly. The most common methods are histogram-based and least-significant bit (LSB) techniques in the spatial domain. Steganographic model is proposed that is based on variable-six LSB insertion to maximize the embedding capacity while maintaining image fidelity.