國內外學者對於資料隱藏技術的研究，已經持續了許多年的時間，近年來出現一個新的研究主題：可回復影像資料隱藏技術，除了可以將隱藏資訊取出之外，還能夠將藏入資料後的影像還原成原始影像，這個技術可以在軍事、醫學，以及法律上產生許多的應用。
我們將影像中的區塊分為兩個集合的像素，分別計算出兩個像素集合的平均值，再利用平均值的差值以及門檻值之間的關係做藏入的動作。
由於一般的可回復影像資料隱藏技術需在無損失環境下才能正確地析出隱藏資料，因此我們也利用多數決資料隱藏的技巧來藏入資料，利用這個技巧，我們的演算法在無損失環境下可以正確析出隱藏之料亦可將藏入資料後的影像還原成原始影像；若是在損失環境下，例如最常見的JPEG壓縮，亦可正確地析出資料。

The research for data hiding has been last for many years. In recent year, a novel topic appeared: reversible data hiding. Except extracting the secret data, this technique can recover the stego-image to cover image. There are many applications for reversible data hiding, such as military, medical, law, and etc.
We group the pixels of block in the image into two groups, calculate the mean values of the two sets of pixels respectively, and then using the relation between the difference of two mean values and the threshold value to embed secret data.
Because general reversible data hiding need to work in lossless environment, we use the majority data hiding skill to embed secret data. Take advantage of this skill, our algorithm could extract the secret data correctly and recover the stego-image into cover image in lossless environment; and extract secret data correctly in lossy environment, such as JPEG compression.

[1] Shih, F.Y.,and Yi-Ta Wu, “A novel fragile watermarking technique,” Multimedia and Expo, 2004. ICME '04. 2004 IEEE International Conference on Volume 2, 27-30 June 2004 Page(s):875 - 878 Vol.2
[2] Li and C.-T., “Digital fragile watermarking scheme for authentication of JPEG images,” Vision, Image and Signal Processing, IEE Proceedings-Volume 151, Issue 6, 30 Dec. 2004 Page(s):460 - 466 Digital Object Identifier 10.1049/ip-vis:20040812
[3] Abdulaziz, N.K., Pang, and K.K., “Robust data hiding for images,” Communication Technology Proceedings, 2000. WCC - ICCT 2000. International Conference on Volume 1, 21-25 Aug. 2000 Page(s):380 - 383 vol.1 Digital Object Identifier 10.1109/ICCT.2000.889233
[4] Ramkumar, M., Akansu, A.N., and Alatan, A.A., “A robust data hiding scheme for images using DFT,” Image Processing, 1999. ICIP 99. Proceedings. 1999 International Conference on Volume 2, 24-28 Oct. 1999 Page(s):211 - 215 vol.2 Digital Object Identifier 10.1109/ICIP.1999.822886
[5] J. M. Barton, “Method and apparatus for embedding authentication information within digital data,” U.S. Patent 5,646,997, 1997.
[6] Yun Q. Shi, Zhicheng Ni, Dekun Zou, Changyin Liang and Guorong Xuan, “Lossless data hiding: Fundamentals, Algorithms and Applications,” ISCAS 2004.
[7] Zhicheng Ni, Yun Q. Shi, Nirwan Ansari and Wei Su, “Reversible Data Hiding,”2003 IEEE.
[8] Jun Tian, “High Capacity Reversible Data Embedding and Content Authentication,” ICASSP 2003.
[9] Jun Tian, “Reversible Data Embedding Using a Difference Expansion,” IEEE TRANSACTIONS ON CIRCUITS AND SYSTEMS FOR VIDEO TECHNOLOGY, VOL.13, NO.8, AUGUST 2003.
[10] Christophe De Vleeschouwer, Jean-Fran□ois Delaigle, and Beno□t Macq, “Circular Interpretation of Bijective Transformation in Lossless Watermarking for Media Asset Management,” IEEE TRANSACTIONS ON MULTIMEDIA, VOL.5, NO.1, MARCH 2003.
[11] Chin-Chen Chang, Wei Liang Tai, and Min-Hui Lin, “A Reversible Data Hiding Scheme with Modified Side Match Vector Quantization,” Proceedings of the 19th International Conference on Advanced Information Networking and Applications (AINA’05).
[12] Hiuk Jae Shim, Jinhaeng Ahn, and Byeungwoo Jeon, “DH-LZW: Lossless Data Hiding in LZW Compression,” 2004 International Conference on Image Precession .
[13] Mehmet U. Celik, Gaurav Sharma, A. Murat Tekalp, Eli Saber, “Reversible Data Hiding,” IEEE ICIP 2002.
[14] Adnan M. Alattar, “Reversible Watermarking Using the Difference Expansion of a Generalized Integer Transform,” IEEE TRANSACTIONS ON IMAGE PROCESSING, VOL.13, NO.8, AUGUST 2004.
[15] Ton Kalker and Frans M.J. Willems, “Capacity Bounds and Constructions for Reversible Data-Hiding,” 2002 IEEE.
[16] Celik et al., “Lossless generalized-lsb data embedding,” IEEE Trans. Image Processing., vol. 14, no. 2, pp. 253–266, 2005.
[17] D. M. Thodi and J. J. Rodriguez, “Reversible watermarking by prediction-error expansion,” Image Analysis and Interpretation, 2004. 6th IEEE Southwest Symposium on, pp. 21–25, 2004.
[18] W. Bender, D. Gruhl, N. Morimoto, and A. Lu “Techniques for data hiding,” IBM Syst. J., vol. 35, no. 3-4, pp. 313-336, 1996.