Tamper Localization in Wavelet Domain Using Semi- Fragile Watermarking

Transcription

1 Tamper Localzaton n Wavelet Doman Usng Sem- Fragle Watermarkng Sandpbha Mangrolya, Ketk Pathak Departement of Electroncs and Communcaton Engneerng Sarvajank College of Engneerng & Technology, Surat Abstract - Ths paper proposes a novel mage authentcaton scheme n the DWT doman. The scheme uses a sem-fragle atermark to detect and precsely locate malcous tamperng regon n mages. The avelet coeffcents selected for embeddng are randomly permuted th a secret key, achevng hgh securty. A bt of the atermark s embedded n a group of coeffcents by means of quantzaton. The expermental results sho, that our algorthm acheves good mage qualty and hgh tamperng detecton resoluton at a lo atermark payload, compared to block-based authentcaton schemes. The atermark s protected aganst local attacks. We have also conducted experments to demonstrate the robustness of the atermark aganst mld to moderate JPEG compresson. Keyord - Multmeda securty, Dgtal atermarkng, Random permutaton, Image authentcaton I. INTRODUCTION II. Dgtal atermarkng can be classfed nto three dfferent categores: robust, fragle and sem-fragle ater-markng. A robust atermark should be able to resst ntentonal or unntentonal manpulatons, hle a fragle atermark s ntended to be destroyed even after the smallest unntentonal manpulaton. Some mportant applcatons for robust atermarkng are fnger prntng, data mnng and copyrght protecton [1, 2]. The thrd category, sem-fragle atermarkng [3, 4], uses atermarks that have the ablty to resst unntentonal manpulatons caused by common mage processng operatons lke JPEG compresson and are fragle aganst ntentonal, malcous manpulatons. The man applcaton feld of fragle and sem-fragle atermarkng s mage and vdeo content authentcaton. Ths paper focuses on usng a sem-fragle atermark for mage authentcaton. Most of the mage authentcaton technques use a block-based concept n the spatal, Dscrete Cosne Transform (DCT) or avelet doman [5, 6] for detectng the tampered regons n the mage. The orgnal mage s parttoned nto blocks, and each block s embedded th ts on atermark usng a secret key. Hoever, most of these schemes are vulnerable to counterfetng attacks and they cannot dscrmnate beteen ntentonal tamperng and unntentonal mage processng dstortons [7, 8]. In such approaches, the tamper detecton resoluton s lmted to the block sze. Smaller block szes and hgher atermark payloads are necessary to mprove the detecton resoluton, resultng n a consderable degradaton of the mage qualty. A specfc attack aganst mage authentcaton s the collage attack, ntroduced by Hollman and Memon n [9]. Usng ths attack, a counterfeter can combne ndependently authentcated blocks to produce forged content. Ths attack s thus undetectable by conventonal block-based atermarkng technques. The scheme proposed n ths paper focuses on elmnatng the drabacks of block-based schemes, usng a Dscrete Wavelet Transform (DWT) based approach and random permutaton of avelet coeffcents. Our algorthm mproves the tamper detecton localzaton; unlke conventonal block-based methods, the exact tampered regon s detected. The atermark payload s sgnfcantly loered, ncreasng the mage qualty. The algorthm can also dstngush beteen ntentonal tamperng and unntentonal mld to moderate JPEG compresson. Mathematcal morphology can be used to mprove the detecton results [10, 11]. The remander of ths paper s organzed as follos. In Secton 2 e present the proposed mage authentcaton scheme n the avelet doman, shong the block dagrams of the atermark encoder and decoder and detalng the steps of the algorthm. Secton 3 contans the expermental results and performances of the proposed scheme and conclusons are gven n Secton 4. THE PROPOSED IMAGE AUTHENTICATION SCHEME IN THE DWT DOMAIN Ths secton descrbes the proposed mage authentcaton scheme. The block dagram of the atermark encoder s shon n Fg. 1. The atermark embeddng process s descrbed n the follong: 1. The orgnal, gray scale mage s transformed nto the avelet doman usng a 2D-DWT decomposton on L resoluton levels. IJEDR Internatonal Journal of Engneerng Development and Research (.jedr.org) 2878

2 Fgure 1. Block dagram of the atermark encoder 2. The detal avelet coeffcents from the LHn, HLn and HHn Wavelet sub-bands of resoluton level n L are selected. For example, n Fg. 2, the coeffcents of the second Wavelet decomposton are chosen for further processng. Selectng hgher resoluton sub-bands for atermark embeddng gves a better tamperng localzaton, but decreases the reslence of the algorthm to common, unntentonal mage processng operatons. LL3 LH3 HL3 HH3 HL2 HL1 LH2 HH2 LH1 HH1 Fgure 2. Wavelet decomposton on L = 3 resoluton levels 3. The selected avelet coeffcents are concatenated n a 1D vector S and randomly permuted usng a secret key K nto a ne vector S. Ths process assures that coeffcents correspondng to the same spatal locaton ll be separated n S. 4. The sequence S of permuted coeffcents s dvded nto groups of d coeffcents. Parameter d controls the atermark payload of the proposed scheme. A atermark bt ll be embedded n every group of d coeffcents. A smaller group sze ll result n a bgger atermark payload and thus n a hgher degradaton of the mage qualty and a smaller sze of the maxmal localzable tampered area, but ll not decrease the detecton resoluton of the scheme. 5. The atermark, a bnary random sequence, s generated and serves as the authentcaton code. has the same length as the number of avelet coeffcent groups. 6. The eghted mean m of every group of permuted avelet coeffcents s obtaned usng the follong equaton: d j 1 ( ) (1) m c j j 1 Where c (j) denotes the j th coeffcent of group. The eght (-1) j s used to make the scheme more robust to common mage processng operatons that, n most cases, change the entre mage and ould not modfy the eghted mean. m 7. The atermarked mean s obtaned by quantzaton of m to the nearest even or odd quantzaton level accordng to the value of the correspondng atermark bt, usng the follong equaton: m / * mod 2 / / * mod 2 / m Q Q f m Q m Q Q Q f m Q (2) IJEDR Internatonal Journal of Engneerng Development and Research (.jedr.org) 2879

3 here [ ] s the nteger part operator and mod2 s the remander after dvson by For every group of coeffcents, the eghted mean m s changed to the atermarked mean by modfyng the avelet coeffcent s,max(j) th the hghest absolute value. Because of the random permutaton operaton every group should have at least one coeffcent th hgh absolute value. The updatng of s, max(j) s done as follos: ( ) ( ) ( ) ( ( )) ( ) (3) ( ) s the atermarked coeffcent and 1 f x 0 sgn( x) 1 f x 0 9. After updatng the coeffcents th the hghest absolute value from every group, the nverse permutaton s appled usng the secret key K. 10. Fnally, the Inverse 2D-DWT s calculated to obtan the atermarked mage. The block dagram of the atermark decoder and mage authentcaton s shon n Fg. 3. The atermark extracton process and mage authentcaton s descrbed n follong: 1. The atermarked, possbly tampered mage s transformed nto the avelet doman usng 2D-DWT decomposton on L resoluton levels. 2. The detal avelet coeffcents from the LHn, HLn and HHn Wavelet sub-bands are selected for atermark extracton. 3. The selected avelet coeffcents are concatenated. Usng a secret key K, the same random permutaton s performed. 4. The sequence of permuted coeffcents s dvded nto groups of d coeffcents. 5. The eghted mean m of every group of coeffcents s calculated usng Eq. (1). 6. A atermark bt ' ' s extracted from the eghted mean of every group of d coeffcents usng Eq. (5). ( ) (5) m (4) Fgure 3. Block dagram of the atermark decoder and mage authentcaton To authentcate the mage the follong step need to be done: 1. Frst, the orgnal atermark s locally generated. If the extracted atermark matches the orgnal one then the mage s authentc. If not, the follong steps ll determne f the mage as tampered. ' 2. If a bt of the extracted atermark does not match the orgnal one, all coeffcents belongng to group are declared as potentally tampered. 3. All coeffcents are permuted back to ther orgnal poston usng the nverse permutaton th the secret key. The coeffcents declared as potentally tampered should be no spread all over the sub-bands. The actual tampered regons IJEDR Internatonal Journal of Engneerng Development and Research (.jedr.org) 2880

4 III. should have a hgh densty of flagged coeffcents. The other flagged coeffcents should be solated and dstrbuted lke random nose. They are false postves and can be clamed as authentc. 4. For a selected resoluton level n e ll have three sub-bands, LHn, HLn and HHn, th flagged and non-flagged coeffcents. We ll construct a bnary authentcaton matrx A of the same sze as the selected sub-bands. A(x,y) = 1 f there s a flagged coeffcent at the same poston (x,y) n any of the HL, LH, or HH selected sub-bands. 5. The solated 1 bts n the authentcaton matrx A ll be removed through flterng. 6. Locatons ncorrectly flagged as tampered are further elmnated by successve eroson and dlaton, usng a dsk of radus R pxels and a square of sze S x S as structural elements. The 1 bts n the fltered and eroded authentcaton matrx should no correctly ndcate the tampered locatons. 7. The flagged postons n A are then mapped back to the spatal doman to ndcate the actual tampered locatons. The senstvty of the tamperng detecton can be adapted by selectng the quantzaton step sze Q, choosng the flter sze n step 5 and the sze of the structural element used for eroson and dlaton n step 6 of the authentcaton process. A larger Q ll ncrease the senstvty, but ll decrease the perceptual qualty of the atermarked mage. A larger flter or a bgger structural element for eroson and dlaton ll reduce the senstvty, but ll also reduce the probablty of false alarms as a result of common mage processng operatons. A trade-off has to be found for specfc applcatons. RESULTS AND ANALYSIS To determne the performances of the proposed mage authentcaton scheme for several mages of dfferent szes ere used. We have evaluated our algorthms n terms of mage qualty, localzaton capablty of the tamperng. Table 1 shos the mage qualty and decodng results of the proposed method for dfferent choces of the avelet resoluton level n for atermark embeddng, quantzaton step sze Q and group sze d, here PSNR s the mean Peak Sgnal to Nose Rato. The PSNR values are above 40 db, except Q=12 (d = 4), Q =16 (d = 4 and d = 8) and Q =20 (d =4, d = 8 and d = 12), here small dstorton are also vsble n the atermarked mages. Quantzaton Level (Q) Table 1 Mean PSNR values for the atermarked mages Image of lena.jpg Image of cameraman.tf Coeffcent N = 1 N = 2 N = 1 N = 2 group sze (d) (PSNR) (PSNR) (PSNR) (PSNR) In Fg. 4 e compare our technque th avelet decomposton level n = 1 and d = 4, d = 8, d = 12 and d = 16. We also measure the PSNR value on dfferent quantzaton level. We can see that our approach acheves very hgh mage qualty th respect to ncreasng group sze (d) and decreasng quantzaton level (Q). IJEDR Internatonal Journal of Engneerng Development and Research (.jedr.org) 2881

5 Fgure III. Graph for qualty of the atermarked mages for dfferent group szes. Next, e test the capacty of our approach to detect the tamperng. For ths purpose, n the mage n Fg.5a shos the orgnal nput mage and Fg.5b shos the atermarked mage. Frst e embed the atermark n the frst Wavelet decomposton level (n = 1), usng groups of d = 8 avelet coeffcents and the quantzaton step sze Q =8. Fg.5c shos the potentally tampered locatons n the mage before refnng the authentcaton result through flterng. (a) (b) (c) (d) IJEDR Internatonal Journal of Engneerng Development and Research (.jedr.org) 2882

6 (e) (f) IV. Fgure 5. (a) orgnal mage, (b) atermarked mage after dong random permutaton and addng atermark bt (c) authentcated mage before flterng for n =1, d = 8 and Q = 8, (d) authentcated mage after flterng and mathematcal morphology operatons for n =1, d = 8 and Q = 8, (e) authentcated mage before flterng for n =2, d = 8 and Q = 8, (f) authentcated mage after flterng and mathematcal morphology operatons for n = 2, d = 8 and Q = 8. Then, e flter the authentcaton matrx th a cross shaped bnary flter of sze F = 5. The fltered authentcaton matrx s then successvely eroded usng a dsk of radus R = 1 and a square of sze 3 x 3 as structural elements. Fg. 5d shos the refned authentcaton result after flterng and eroson operatons. In Fg. 5e and f e depct the authentcaton results before and after refnement usng the follong parameters: n =2, d = 8 and Q = 8. CONCLUSION In ths paper e have proposed a ne mage authentcaton scheme usng a sem-fragle atermark that can detect and locate malcous tamperng n mages. The embeddng and extracton of the authentcaton atermark s done n the DWT doman. Our technque acheves hgh mage qualty and hgh tamperng detecton resoluton at a lo atermark payload usng random permutaton of the avelet coeffcents before embeddng, the atermark s also protected aganst local attacks. REFERENCES [1] R.O. Preda, D.N. Vzreanu, Robust avelet-based vdeo atermarkng scheme for copyrght protecton usng the human vsual system, Journal of Electronc Imagng, vol. 20, pp , [2] R.O. Preda, D.N. Vzreanu, A robust dgtal atermarkng scheme for vdeo copyrght protecton n the avelet doman, Measurement, Measurement, vol. 43, pp , [3] Preda, R.O.; Vzreanu, D.N., "Blnd Watermarkng Capacty Analyss of MPEG2 Coded Vdeo," 8th Internatonal Conference on Telecommuncatons n Modern Satellte, Cable and Broadcastng Servces, pp. 465,468, Sept [4] A. Pva, F. Bartoln, R. Caldelly, Self recovery authentcaton of mages n DWT doman, Internatonal Journal of Image and Graphcs, vol. 5, pp , [5] C.-T. L, H. S, Wavelet-based fragle atermarkng scheme for mage authentcaton, Journal of Electronc Imagng, vol. 16, pp. 1-9, [6] A.H. Ouda, M.R. El-Sakka, Localzaton and securty enhancement of blockbased mage authentcaton, IEEE Internatonal Conference on Image Processng, vol. 1, pp , September 2005 [7] C. Fe, D. Kundur, R.H. Kong, Analyss and desgn of secure atermark-based authentcaton systems, IEEE Transactons on Informaton Forenscs and Securty, vol. 1, pp , 2006 [8] L.P. Frere, P. Comesana, J.R.T. Pastorza, F.P. Gonzalez, Watermarkng securty: a survey, LNCS Transactons on Data Hdng and Multmeda Securty, vol. 1, pp , [9] M. Hollman, N. Memon, Counterfetng attacks on oblvous block-se ndependent nvsble atermarkng schemes, IEEE Transactons Image Processng, vol. 9, pp , [10] D. N Vzreanu, S. Halunga, G. Marghescu, Morphologcal skeleton decomposton nterframe nterpolaton method, Journal of Electronc Imagng, vol. 19, pp. 1-3, [11] R. M Udrea, D.N. Vzreanu, Iteratve generalzaton of morphologcal skeleton, Journal of Electronc Imagng, vol. 16, pp. 1-3, IJEDR Internatonal Journal of Engneerng Development and Research (.jedr.org) 2883