steganographic method based upon JPEG and quantization table modiﬁcation
In this paper, a novel steganographic method based on joint photographic expertgroup (JPEG) is proposed. The proposed method modiﬁes the quantization table ﬁrst. Next, the secret message is hidden in the cover-image with its middle-frequency of the quantized DCT coeﬃcients modiﬁed. Finally, a JPEG stego-image is generated. JPEG is a standard image and popularly used in Internet. The stego-image will not be suspected if we could apply a JPEG image to data hiding. We compare our method with a JPEG hiding-tool Jpeg–Jsteg. From the experimental results, we obtain that the proposed method has a larger message capacity than Jpeg–Jsteg, and the quality of the stegoimages of the proposed method is acceptable. Besides, our method has the same security level as Jpeg–Jsteg.
Joint photographic expert-group (JPEG)  is a famous ﬁle for images. It applies the discrete cosine transformer (DCT) to image content transformation. DCT is a widely used tool for frequency transformation. If we apply JPEG images to data hiding, the stego-image will not easily draw attention of suspect. There is a JPEG hiding-tool Jpeg–Jsteg . In the Jpeg–Jsteg embedding method, secret messages are embedded in the least signiﬁcation bits (LSB) of the quantized DCT coeﬃcients whose values are not 0, 1, or )1. The main drawback of Jpeg–Jsteg is less message capacity. This is because, after the DCT transformation and quantization of JPEG, the coeﬃcients are almost all zero and cannot hide messages according to the deﬁnition of Jpeg–Jsteg. To improve the message capacity of Jpeg–Jsteg, a new data hiding method based on JPEG and quantization table modiﬁcation is proposed. Our method was inspired by Hsu and Wu’s approach . Obviously, their scheme is aimed for the image copyright protection against illegal use by attackers while ours is aimed for security hiding image in a plain image. Again, we shall emphasize here that our method, the attacker is unable to retrieve secret messages form the plain image in which they were hidden. So he does not know the contents of secret image unless he has the ability to decipher the plain image. As for Hsu and Wu’s approach, they propose a very robust watermarking technique in which the attacker is unable to remove or severely destroy the hidden watermarks even he knows what the contents of watermarks. From the above statements, we know that Hsu and Wu’s approach, the contents of the hidden images (watermarks) are not secret data while in ours, they are. T