High Payload Reversible Data Hiding Scheme Using Difference Segmentation and Histogram Shifting

Transcription

1 JOURNAL OF ELECTRONIC SCIENCE AND TECHNOLOGY, VOL. 11, NO. 1, MARCH Hgh Payload Reversble Data Hdng Scheme Usng Dfference Segmentaton and Hstogram Shftng Yung-Chen Chou and Huang-Chng L Abstract Steganography s a technque that conceals secret data nto a cover medum for delverng secret data over publc computer networks. Reversble data hdng schemes not only can acheve secret data delvery, but also can restore the cover medum. Hstogram shftng s one of the most popular reversble data hdng technques. Luo et al. presented a reversble data hdng technque that shfts the hstogram of predcton error. But the embeddng payload of Luo et al. s method can further be mproved. The proposed method uses a dfference segmentaton strategy and pseudo pxel generaton to ncrease the heght of peak n the predcton error hstogram. The expermental results show that the embeddng payload of the proposed method s hgher than that of Luo et al. s method. Index Terms Data hdng, hstogram sftng, secret data delvery, steganography. 1. Introducton Tradtonally, prvate data can be securely delvered to the recever by adoptng a cryptosystem. The cryptosystem generates keys to encrypt/decrypt prvate data. Usng an encryptng procedure makes encrypted prvate data look lke random nose. Encrypted data make t hard for an unntended user to know the nformaton wthout rght keys. Therefore, only the ntended recever wth the correct decrypton key can fully decrypt the cpher data nto plantext. However, usng a cryptosystem to assst secret data delvery has two drawbacks. Frst, the encrypton process may lead to a hgh computaton cost due to a large sze of secret nformaton. Second, the secret data delveres may fal f an unexpected user ntercepts the cpher data Manuscrpt receved June 4, 2012; revsed July 25, Ths work was supported by Asa Unversty under Grant No. 100-asa-33. Y.-C. Chou s wth the Department of Computer Scence and Informaton Engneerng, Asa Unversty, Tachung 41354, Tawan (Correspondng author e-mal: yungchen@asa.edu.tw H.-C. L s wth the Department of Computer Scence and Informaton Engneerng, Asa Unversty, Tachung 41354, Tawan (e-mal: st @gmal.com Dgtal Object Identfer: /j.ssn X transmsson. Because the unexpected user s nterested n the cphertext even t looks lke meanngless random nose. Steganography s another method of secret data delvery. The man concept of steganography s to use a cover medum to cover the cpher data and delver the stego medum to the recever va publc computer networks. The beneft of steganography s that an unexpected user wll see a meanngful stego medum wth mperceptble dstorton. Thus, the unexpected user wll be deceved. From ths pont of vew, the nconspcuous dfferences are one of the most mportant factors for desgnng a data hdng scheme. Several dfferent meda can play the cover medum n the steganography technque. Generally, a cover medum can be the text, audo, HTML fle, vdeo, mage, or program code. Here, we use an mage as the cover medum n the proposed data hdng scheme. Steganography technques can be brefly classfed nto spatal nconspcuous dfferences, frequency doman, and compresson doman. The spatal doman method tres to conceal secret data nto a dgtal mage by modfyng pxels values n a cover mage for mplyng secret messages [1]. Spatal doman data embeddng s easy to mplement and carres a low computaton cost. The frequency doman data hdng scheme focuses on modfyng coeffcents for mplyng secret data. Generate the mage s coeffcents by applyng transformaton functons (e.g., dscrete cosne transform, dscrete wavelet transform, etc. to transform pxel values nto coeffcents. The frequency doman s tme consumng and the embeddng payload s lmted. But one of the benefts of the frequency doman data hdng technque s that the stego mages have better vsual qualty than the spatal doman data hdng method. To save the storage cost and transmsson bandwdth, data compresson can sgnfcantly reduce the sze of dgtal mages. The compresson doman data hdng technque modfes the compresson procedure for mplyng the secret data n the compresson code [2],[3]. Reversblty s an mportant aspect of secret data delvery n recent years. In some nsttutons, such as mltary and dstance medcal treatment, applcatons requre restorng the orgnal cover mage. Thus, reversble data hdng means a cover mage carryng some secret message va a reversblty scheme. Then the recever not only can extract the secret message, but also can fully restore the cover mage back to the orgnal one [4] [7].

2 10 JOURNAL OF ELECTRONIC SCIENCE AND TECHNOLOGY, VOL. 11, NO. 1, MARCH 2013 Several strateges can acheve the goal of data hdng reversblty. These strateges can be classfed nto frequency transformaton, dfferences expanson, and hstogram shftng. Vleeschouwer et al. used hstogram shftng to conceal secret data nto a cover mage [7]. Vleeschouwer et al. s method classfes pxels n a cover mage nto two sets of crcularly nterpolatng hstograms, and then shfts the hstograms to conceal secret data. N et al. presented a reversble data hdng method that analyzes the pxel dstrbuton n a cover mage to generate the pxel hstogram [8]. And, peak and zero ponts were found by scannng the hstogram then shftng the hstogram for concealng secret data. Hwang et al. proposed a data hdng technque wth reversblty by extendng N et al. s method [9]. Hwang et al. s method utlzed extra nformaton to remember the restorng nformaton, thus the cover mage stll can be restored. Ln and Hsueh proposed a reversble data hdng technque by usng bn exchange to modfy hstograms [10]. Ln and Hsueh s successful method ncreased the pure embeddng payload and acheved lower dstorton of stego mages. Further, Km et al. presented a reversble data hdng scheme by selectng two peak ponts and two zero ponts to mprove the embeddng payload performance [5]. Then, Luo et al. utlzed the pxel predcton strategy to generate predcted pxels to ncrease the heght of peak n predcton error hstograms [11]. Because the predcton error s sgnfcantly narrowed down n a lmted range, the heght of peak pont has been ncreased and the embeddng payload has been mproved. However, the embeddng payload of Luo et al. s method can stll be mproved. The embeddng payload of hstogram shftng data hdng schemes s hghly related to the heght of peak pont and the number of peak ponts they use. On the other hand, for achevng reversblty, some extra nformaton (.e., peak ponts and zero ponts needs to be stored. The proposed method uses a dfference segmentaton strategy and predcton error to ncrease the heght of peak pont n order to obtan a hgher embeddng payload. Also, the proposed method does not need to remember any peak pont or zero pont nformaton. 2. Related Works Luo et al. presented a data hdng technque usng hstogram shftng, n whch the secret data s embedded nto a cover mage by applyng a hstogram modfcaton strategy [11]. Luo et al. s man dea s usng predefned sample pxels to predct pxels for generatng predcton error. The key steps of Luo et al. s method are descrbed as follows. For smplcty, a cover mage s denoted as I={p, j =1, 2,, H, j=1, 2,, W} and p, j {0, 1,, 255}, where H and W represent the heght and wdth of the cover mage I, respectvely. Frst, the margnal pxels n the cover mage are reserved for concealng the extra data used for secret data extracton and mage restoraton. The extra data s concealed nto the margnal pxels by usng least sgnfcant bts (LSB replacement. Because the margnal pxels wll be modfed, thus the orgnal LSB data of margnal pxels are collected for concealng nto sample pxels. Second, Luo et al. s method generates predcton three tmes, namely Level 1 predcton, Level 2 predcton, and Sample pxel predcton. Note that all of the predcton processes are just for the remanng pxels (.e., all pxels except margnal pxels. The frst predcton focuses on Level 1 pxels, whch are predcted by usng ts neghborng sample pxels. The sample pxels come from ts 45 and 135 drectons. For example, let the current Level 1 pxel be p, j and predcted value p, j s generated by adoptng (1 (5: p, j= w45μ45 + w135μ135 (1 μ45 = ( p 1, j+ 1 + p+ 1, j 1 2 μ135 = ( p 1, j 1 + p+ 1, j+ 1 2 (2 μ = ( μ45 + μ135 2 (3 w45 = σ45 ( σ45 + σ135 w135 = σ135 ( σ45 + σ135 (4 σ45 = ( p 1, j+ 1 μ + ( p+ 1, j 1 μ σ135 = ( p 1, j 1 μ + ( p+ 1, j+ 1 μ (5 where μ 45 and μ 135 represent the mean values of sample pxels n 45 and 135 drectons correspondng to p, j, respectvely. Then, after the Level 1 pxels predcton has been done, the Level 2 pxels can be predcted by referrng to ts neghborng sample pxels and Level 1 predcted pxels usng (6 (10: p, j= w90μ90 + w180μ 180 (6 μ90 = ( p 1, j + p+ 1, j 2 μ180 = ( p, j 1 + p, j+ 1 2 (7 μ = ( μ90 + μ180 2 (8 w90 = σ90 ( σ90 + σ180 w180 = σ180 ( σ90 + σ180 (9 σ90 = ( p 1, j μ + ( p+ 1, j μ σ180 = ( p, j 1 μ + ( p, j+ 1 μ (10 where μ 90 and μ 180 represent the mean values pxels of 90 and 180 drectons correspondng to p, j, respectvely. Then, the predcton error s the dfference between the orgnal pxel and the predcted pxel. When the predcton errors have been calculated, the next step s analyzng the dfferences to generate a hstogram. After that, secret data

3 CHOU et al.: Hgh Payload Reversble Data Hdng Scheme Usng Dfference Segmentaton and Hstogram Shftng 11 can be embedded by applyng the hstogram modfcaton strategy. Further, the predcted values of sample pxels are predcted by referrng to stego Level 1 and Level 2 pxels. Here, sample pxels are used to conceal the nformaton about reserved LSB bts of the margnal pxels. Agan, the predcton works by usng (6 (10. The embeddng procedure for sample pxels stll adopts hstogram modfcaton. Because the hstogram shftng strategy requres rememberng the peak and the zero ponts, the extra nformaton s embedded nto the reserved margnal pxels by usng LSB replacement. For data extracton on the recever sde, the rght recever can extract the secret data from the stego mage wth the secret data extractng procedure. Frst, the extra nformaton s extracted by drectly takng LSB from the margnal pxels. Then, the same predcton method s adopted to generate the predcton values for sample pxels. After the sample pxels predcton, the error hstogram has been generated, and then the orgnal margnal LSB data can be extracted by referrng to the extra nformaton. Accordng to the property of hstogram modfcaton, the sample pxels can be fully reconstructed. Then, the Level 1 and Level 2 pxels predcton procedures are adopted to generate the predcton pxels. Agan, the predcton error hstogram of Level 1 and Level 2 pxels wth the extra nformaton s used to extract secret data. The Level 1 and Level 2 pxels can be fully restored, too. 3. Proposed Method 3.1 Data Embeddng The property of a natural mage contans a local area wth smlar pxels dstrbuton, so the predcton error wll be narrowed down to a small range, whch wll help ncrease the heght of the hstogram. In other words, the heght of the peak pont wll be ncreased. The proposed method contans three man phases, namely: pxel adjustment, predcton error generaton, and data embeddng. Pxel adjustment s needed to prevent ambguous results on the data extractng sde. Then, pseudo pxels are generated by calculatng the mean values of segments n a block. Here, the segments wll be generated by segmentng the dfference between the mum value and mnmum value n a block. Then, the predcton error s generated by calculatng the dfference between the pxel value and pseudo pxel value. After the predcton errors have been generated, secret data s embedded nto the cover mage by applyng the hstogram shftng strategy. Because the local area has smlar pxels dstrbuton, the proposed method dvdes a cover mage nto non-overlappng blocks wth the sze of n n. For smple descrpton, let the cover mage I={p =1, 2,, H W}, where H and W are the heght and wdth of the mage and p {0, 1,, 255}. After dvson, the mage s also represented as I={B =1, 2,, NB}, where NB refers to the total number of mage blocks and B ={x j j =1, 2,, n n}. For achevng securty, the secret data wll be encrypted as cpher text by usng any crypto system. Thus, the unexpected user can not read real secret messages even f the user has extracted secret nformaton from the stego mage. The cpher text s denoted as M={b =1, 2,, NM}, where NM s the total bts of cpher text and b {0, 1}. Actually, the fnal embedded data S concatenate NE, M, and RB together, also denoted as S=NE M RB, where s the concatenate operaton. Here, NE and RB are the non-embeddable blocks nformaton and frst block s LSB data. To avod the underflow and overflow problems, some blocks wll be defned as non-embeddable blocks. Here, the underflow problem occurred when the pxel value s close to 0, and the pxel value mght become a negatve value due to secret data embeddng. The overflow problem occurrs when the pxel value s closest to the mum gray value (.e., the mum value of a 8-bts gray pxel s 255 and the pxel value mght become greater than the mum gray value due to secret data embeddng. If a block satsfes one of followng cases, then the block s a non-embeddable block that wll not be used for concealng secret data. Let the block s mum pxel value and mnmum pxel value be generated by B = { x B } and j mn B = mn{ x j B }, respectvely. The dfference between the mum value and mnmum value s generated by mn D = B B. N seg s the number of segments. Case 1: f D N seg, then do nothng. Case 2: f mn mn B 3Nseg 2, then add B nto mn extra nformaton and set B as 0. Case 3: B 255 3Nseg 2, then add (255 B nto extra nformaton and set B as 255. If a block satsfes Case 1, then the block s a smooth block wth smlar pxels dstrbuton and the block wll do nothng. Case 2 and Case 3 are the cases of underflow and overflow, thus the block wll not be used for concealng secret data. For an embeddable block, calculate the dfference D and segment D nto N seg segments. In order to prevent ambguous results n the data extractng phase, pxel adjustment s needed. Frst, a new mnmum B mn and new mum respectvely. B B are calculated by usng (11 and (12, B = B 3N 2 (11 mn mn mn B 3Nseg 2 1, f mod( Nseg, 2==1 = (12 mn B 3Nseg 2, otherwse. seg

4 12 JOURNAL OF ELECTRONIC SCIENCE AND TECHNOLOGY, VOL. 11, NO. 1, MARCH 2013 Fg. 1. Illustrate of hstogram shftng. The orgnal pxels can also be adjusted nto new pxel values. The start pxel value of the frst segment s mn B +3. The end pxel value of last segment s B 2. Otherwse, create a gap (.e., the gap s 4 between two segments. Then, the length of the segment s determned by mn ( B B N seg. The pseudo pxel y k of the kth mn segment s determned by yk = ( segk + segk 2, mn where seg k and seg k are the mum and mnmum values n the segment, respectvely. Next, generate the predcton error by calculatng the dfference between the pxel and correspondng pseudo pxel values. After all of the predcton errors have been generated, create the predcton error hstogram by countng the dfference values from the whole mage. To observe the result of dfference hstogram, we found that the three hghest peaks are 1, 0, and 1. Thus, 1, 0, and 1 are set as the default peaks. Then, the predcton error s less than or equal to 2 s decreased by two. The predcton error that s equal to 1 s shfted to 2. The predcton error greater than or equal to 2 s ncreased by one. Fg. 1 llustrates the hstogram adjustment concept. After that, f the predcton error s equal to 2, 0, or 1 and secret bt b =0, then do nothng. If b =1, and the predcton error s equal to 2, 0, or 1, then adjust the predcton error to 3, 1, and 2, respectvely. If the predcton error s not equal to 2, 0, or 1, then keep the predcton error wthout any change. And generate the stego pxel by usng a pxel s correspondng pseudo pxel plus the predcton error. Fnally, the nformaton regardng the number of non-embeddable blocks s remembered n the frst block by usng LSB (least sgnfcant bts replacement. 3.2 Data Extractng Data extractng s a reverse process of data embeddng. Frst, extract the non-embeddable block numbers from the frst block s LSB. Then, extract data from the remanng blocks. Every remanng block must belong to one of followng cases. mn Case I. If D = ( B B Nseg, then no secret data can be extracted. Case II. If B mn = 0, then no secret data can be extracted and restore bts from S. B mn by takng log2( 3Nseg 2 Case III. If B = 255, then no secret data can be extracted and restore log 3N 2 B by takng 2( seg bts from S. Case IV. The block does not belong to any of the above three cases. For a block belongs to Case IV (.e., an embeddable block, calculate D and segment D nto N seg segments. Then, calculate each segment s pseudo pxel and generate the predcton error by calculatng the dfference between the stego pxel and pseudo pxel. After that, secret data can be extracted by usng followng rules. Rule 1. If the predcton error s equal to 3, then output a secret bt 1 and restore the predcton error as 1. Rule 2. If the predcton error s equal to 2, then output a secret bt 0 and restore the predcton error as 1. Rule 3. If the predcton error s equal to 1, then output a secret bt 1 and restore the predcton error as 0. Rule 4. If the predcton error s equal to 0, then output a secret bt 0. Rule 5. If the predcton error s equal to 2, then output a secret bt 1 and restore the predcton error as 1. Rule 6. If the predcton error s equal to 1, then output a secret bt 0. Rule 7. If the predcton error s smaller than or equal to 4, then no secret data can be extracted, so restore the predcton error by addng 2 to the predcton error. Rule 8. If the predcton error s greater than or equal to 3, then no secret data can be extracted, so restore the predcton error by subtractng 1 from the predcton error. Further, the frst block s LSB s restored by referrng to 2 bts of the extracted secret data. Fnally, the rght recever wth a decrypton key wll gan the real secret data by decryptng the extract message. Also, the stego mage can be fully restored. the least log ( n n 4. Expermental Results To evaluate the performance of the proposed method, the proposed method and Luo et al. s method are mplemented usng Octave v3.24 software works on a Lnux platform. In order to test the effect of the proposed method for dfferent mages, nne commonly tested mages are used n our smulatons. Fg. 2 shows the test gray-scale mages szed pxels. The vsual qualty of stego mage and embeddng payload are the two most mportant factors for evaluatng the performance of a data hdng technque. As we know, evaluatng the vsual qualty through humans eyes s effectve, but t s very subjectve. To avod observaton bas, we use the peak sgnal-to-nose rato (PSNR for evaluaton, whch s an objectve vsual qualty measurement. Normally, a hgh PSNR ndcates that the

5 CHOU et al.: Hgh Payload Reversble Data Hdng Scheme Usng Dfference Segmentaton and Hstogram Shftng 13 stego mage s the most smlar to ts orgnal mage. Contrarly, a small PSNR value ndcates that the stego mage contans large dstortons that are dssmlar to ts orgnal cover mage. Generally, t s hard for a user to dentfy the dstorton from the stego mage by eyes when the PSNR value s greater than 30 db. Further, the embeddng payload s used to evaluate the total number of secret bts embedded n a cover mage. A data hdng scheme wth a small embeddng payload needs to send more dfferent stego mages than a hgh embeddng payload scheme for the same secret data sze. Sendng too many dfferent stego mages wll attract unexpected users to pay more attenton on transmsson. Here, the embeddng payload s used to count the total bts embedded nto a cover mage, defned as ep= S. Because the proposed method needs to remember the nformaton of non-embeddable blocks, the pure embeddng payload s calculated by ep p =ep NE, where the operaton s calculatng the total bts and NE represents the extra nformaton of non-embeddng blocks. Fg. 3 shows the PSNR comparson for testng dfferent segment numbers. From the expermental result, Luo et al. s method has better PSNR outcomes, whch s reasonable because t conceals more secret data than the proposed method. Also, all of PSNR values of stego mages are hgher than 30 db. Further, usng lesser segments wll get better PSNR outcomes. Fg. 4 shows the embeddng payload comparson results for testng dfferent segment numbers. From expermental results, complex content mages (e.g., Baboon acheve a hgher embeddng payload when the segment number s ncreased. Contrary, smooth content mages wll get a lower embeddng payload when the segment number s ncreased. Ths stuaton s reasonable, because a smooth content mage contans more smooth blocks, thus the number of non-embeddable blocks wll be ncreased when ncreasng the segment number. For the expermental results, we can conclude that 4 or 5 are the sutable segment number. (a (b (c (d (e (f (g (h ( Fg. 2. Test mages: (a Baboon, (b Barbara, (c Boat, (d Goldhll, (e Jet(F16, (f Lena, (g Salboat, (h Tffany, and ( Zelda. PSNR Luo et al. N seg =2 N seg =3 N seg =4 N seg =5 N seg =6 25 Baboon Barbara Boat Goldhll Jet(F16 Lena Salboat Tffany Zelda Images Fg. 3. PSNR comparson for dfferent segment numbers (block sze 4 4 pxels Pure embedded bts Luo et al. N seg =2 N seg =3 N seg =4 N seg =5 N seg =6 0 Baboon Barbara Boat Goldhll Jet(F16 Lena Salboat Tffany Zelda Images Fg. 4. Embeddng capacty comparson for dfferent segment numbers (block sze 4 4 pxels N seg =2 N seg =3 5 N seg =4 N seg =5 N seg =6 4 Number of non-embeddable blocks Baboon Barbara Boat Goldhll Jet(F16 Lena Salboat Tffany Zelda Images Fg. 5. Non-embeddable blocks comparson for dfferent segment numbers (block sze 4 4 pxels. Fg. 5 shows analyss results of non-embeddable blocks n dfferent segment number settngs. Generally, ncreasng the number of segments wll acheve a hgher embeddng payload. From the expermental results we found that the complex content mage (e.g., Baboon has a lower mpact n changng the number of segment settng. On the contrary, a smooth content mage (e.g., Jet(F16 s sgnfcantly mpacted by changng the number of segment settngs.

6 14 JOURNAL OF ELECTRONIC SCIENCE AND TECHNOLOGY, VOL. 11, NO. 1, MARCH Conclusons Data hdng technques make t easer to deceve the unexpected user for achevng the goal of secret data delvery. The proposed reversble data embeddng technque utlzes dfference segmentaton to dvde the dfference between the mum pxel and mnmum pxel nto several segments. Thus, the hstogram of predcton error wll be sgnfcantly ncreased, whch helps ncrease the embeddng payload performance. Also, the proposed method does not need to remember the nformaton about the peak and zero ponts because the peak ponts are fxed as 1, 0, and 1. The expermental results show that the proposed method has hgher embeddng payload performance than Luo et al. s method. References [1] Y.-C. Chou, C.-C. Chang, and K.-M. L, A large payload data embeddng technque for color mages, Fundamenta Informatcae, vol. 88, no. 1 2, pp , [2] C.-C. Chang, T.-D. Keu, and Y.-C. Chou, Reversble nformaton hdng for VQ ndces based on locally adaptve codng, Journal of Vsual Communcaton and Image Representaton, vol. 20, no. 1, pp , Jan [3] Y.-C. Chou and H.-H. Chang, A hgh payload data hdng scheme for color mage based on BTC compresson technque, n Proc. of the 4th Int. Conf. on Genetc and Evolutonary Computng, Shenzhen, 2010, pp [4] J. M. Barton, Method and apparatus for embeddng authentcaton nformaton wthn dgtal data, U.S. Patent , [5] K. S. Km, M. J. Lee, H. Y. Lee, and H. K. Lee, Reversble data hdng explotng spatal correlaton between sub-sampled mages, Pattern Recognton, vol. 42, no. 11, pp , [6] C.-Y. Ln and C.-C. Chang, Hdng data n VQ-Compressed mages usng dssmlar pars, Journal of Computers, vol. 17, no. 2, pp. 3 10, [7] C. D. Vleeschouwer, J. F. Delagle, and B. Macq, Crcular nterpretaton of bjectve transformaton n lossless watermarkng for meda as management, IEEE Trans. on Multmeda, vol. 5, no. 1, pp , [8] Z. N, Y. Q. Sh, N. Ansar, and S. We, Reversble data hdng, IEEE Trans. on Crcuts System Vdeo Technology, vol. 16, no. 3, pp , [9] J. Hwang, J.-W. Km, and J.-U. Cho, A reversble watermarkng based on hstogram shftng, n Proc. of Int. Workshop on Dgtal Watermarkng, Sprnger-Verlag, Jeju Island, 2006, pp [10] C.-C. Ln and N.-L. Hsueh, A lossless data hdng scheme based on three-pxel block dfferences, Pattern Recognton, vol. 41, no. 4, pp , [11] L. Luo, Z. Chen, M. Chen, X. Zeng, and Z. Xong, Reversble mage watermarkng usng nterpolaton technque, IEEE Trans. on Informaton Forenscs and Securty, vol. 5, no. 1, pp , Yung-Chen Chou receved the B.S. degree n management nformaton systems from Natonal Pngtung Unversty of Scence & Technology, Pngtung, Tawan n 1998, and the M.S. degree n nformaton management from Chaoyang Unversty of Technology, Tachung, Tawan n He receved the Ph.D. degree n computer scence and nformaton engneerng from the Natonal Chung Cheng Unversty, Chay, Tawan n Snce February 2009, he has been an assstant professor wth Asa Unversty, Tachung, Tawan. Hs current research nterests nclude steganography, watermarkng, and mage processng. Huang-Chng L was born n Tawan. He currently s pursung the B.S. degree wth the Department of Computer Scence and Informaton Engneerng, Asa Unversty, Tachung, Tawan. Hs research nterests nclude mage processng and steganography.