a2) United States Patent
`US 7,133,534 B2
`(10) Patent No.:
`Epstein et al.
`Nov.7, 2006
`(45) Date of Patent:
`
`US007133534B2
`
`(54) COPY PROTECTION VIA REDUNDANT
`WATERMARK ENCODING
`
`(75)
`
`Inventors: Michael A. Epstein, Spring Valley, NY
`(US); Robert M. McDermott,
`Montross, VA (US)
`
`(73) Assignee: Koninklijke Philips Electronics N.V.,
`Eindhoven (NL)
`
`(*) Notice:
`
`Subject to any disclaimer, the term ofthis
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 628 days.
`
`Appl. No.: 10/233,454
`
`Filed:
`
`Sep. 3, 2002
`
`Prior Publication Data
`
`US 2004/0042635 Al
`
`Mar. 4, 2004
`
`Int. Cl.
`
`
`
`21)
`
`22)
`
`65
`
`51)
`
`56
`
`
`
`(2006.01)
`GO6K 9/00
`52) US. C1. ceccccccccccceesceseseeceesesessesesenenseees 382/100
`58)
`Field of Classification Search ................... None
`
`See application file for complete search history.
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`........0.... 382/100
`9/2002 Rhoads et al.
`2002/0122564 A1*
`2002/0149976 A1* 10/2002 Sako .......0..
`
`2003/0025423 Al*
`2/2003 Miller etal.
`.. 312/100
`3/2003 Carr et al. oe 713/176
`2003/0056104 Al*
`2003/0070075 Al*
`4/2003 Deguillaumeetal. ...... 713/176
`2003/0128860 Al*
`7/2003 Braudawayet al.
`........ 382/100
`2003/0223099 A1* 12/2003 Fan et al. wc 358/537
`
`2005/0254684 Al* 11/2005 Rhoads ........cc eee 382/100
`
`FOREIGN PATENT DOCUMENTS
`
`EP
`JP
`WO
`
`0984616 A2
`2003022389
`WO00173997
`
`*
`
`3/2000
`1/2003
`10/2001
`
`* cited by examiner
`
`Primary Examiner—Samir Ahmed
`Assistant Examiner—Oneal R Mistry
`(74) Attorney, Agent, or Firm—Larry Liberchuk
`
`(57)
`
`ABSTRACT
`
`A watermark is encoded redundantly so as to provide
`effective copy protection. To assure a reliable detection of
`the watermark in the presence of a potentially faulty water-
`mark detection process, some or all of the watermark is
`redundantly encoded. The number of redundant encodings
`of the watermark is selected so that upon modification of the
`watermarked material, sufficient redundancy exists so that
`the material can be identified as watermarked material, and
`the number of detected copies of the watermark is used to
`detect the modification. Statistical processes are employed
`to determine the presence or absence of the watermarks in
`the presence of a potentially faulty watermark detection
`process. Different criteria may be applied to the watermark
`detection process for the verification of the watermarked
`portions, based on the desired degree of confidence for
`determining whether the appropriate watermarkis present or
`absent, and the desired degree of confidence for determining
`whether a modification has occurred.
`
`
`
`14 Claims, 2 Drawing Sheets
`
`......... 382/183
`5/2000 Bhaskaran et al.
`6,064,764 A *
`2200] TtO aanuenwaweawen 382/100
`6,192,139 Bl
`/2001 Cox et al.
`6,208,735 Bl
`6/2001 Nakamura et al.
`6,246,775 Bl
`6/2001 Linnarts
`6,252,972 Bl
`(2001 Cox et al. ee 382/100
`6,278,792 Bl*
`2002 Chen et al.
`...
`6,396,937 B1*
`369/47 .12
`2/2004 Sako
`6,697,306 BI*
`.» 382/100
`6/2004 Rhoadset al.
`6,744,906 B1*
`....
`w 709/229
`
`6,820,125 B1* 11/2004 Diaset al.
`....
`« 713/176
`2002/0053026 Al*
`5/2002 Hashimoto.......
`‘
`
`7/2002 Nakamura etal. .......... 713/176
`2002/0095577 A1*
`
`« 382/100
`
`
`REDUNDANT
`WATERMARKED
`WATERMARK
`MATERIAL
`
`
`ENCODER
`100
`
`CONTENT
`
`MATERIAL
`
`REDUNDANCY
`CONTROLLER
`
`110
`
`Sony Exhibit 1024
`Sony Exhibit 1024
`Sony v. MZ Audio
`Sony v. MZ Audio
`
`

`

`U.S. Patent
`
`Nov.7, 2006
`
`Sheet 1 of 2
`
`US 7,133,534 B2
`
`120
`
`CONTENT
`MATERIAL
`
`100
`
`REDUNDANT
`WATERMARK
`ENCODER
`
`WATERMARKED
`CONTENT
`MATERIAL
`
`
`
`
`
`REDUNDANCY
`
`CONTROLLER
`FIG. 1
`
`110
`
`WATERMARKED
`CONTENT
`MATERIAL
`
` 210
`
`WATERMARKED
`TESTER
`
`200
`
`240
`
`RENDERING
`SYSTEM
`
`
`
`
`
`

`

`U.S. Patent
`
`Nov.7, 2006
`
`Sheet 2 of 2
`
`US 7,133,534 B2
`
`INITIALIZE
`count-0
`
`P73
`
`
`
`CONDUCT
`WATERMARK
`TEST
`
`WATERMARK?
`
`
`
`320
`
`330
`
`>E®
`
`INCREMENT
`COUNT
`
`1-340
`
`
`
`i
`
`350
`
`YES
`
`360
`
`NO
`
`UNPROTECTED
`
`COMPARE COUNT TO
`E(C|p) AND E(Cr)
`E(C|p)
`
`\
`
`E(C|r)
`
`
`
`70 UNALTERED)(ALTERED
`
`390
`
`395
`
`HG. 3
`
`

`

`US 7,133,534 B2
`
`2
`watermark. Additionally, each of the watermark processes
`must be configured so that they do not interfere with each
`other.
`
`BRIEF SUMMARY OF THE INVENTION
`
`It is an object of this invention to provide a robust and
`reliable copy protection scheme that accommodatesa detec-
`tion of a modification to the watermarked material. but does
`not require the use of multiple watermarking processes. It is
`a furtherobject of this invention to provide a copy protection
`schemethat is fault tolerant.
`
`These objects and others are achieved by the use of a
`watermark that has multiple degrees of redundancy. To
`assure a reliable detection of the watermark in the presence
`of a potentially faulty watermark detection process, some or
`all of the watermark is redundantly encoded. Wheneverthe
`watermarked material is modified, the quality of the water-
`mark decreases, and the likelihood of each redundant copy
`of the watermark being detected by a watermark detector
`decreases. The numberof redundant encodingsof the water-
`mark is selected so that upon modification of the water-
`marked material, sufficient redundancyexists so that the
`material can be identified as watermarked material, and the
`numberof detected or undetected copies of the watermark is
`used to detect the modification. Statistical processes are
`employed to determine the presence or absence of the
`watermarksin the presenceofa potentially faulty watermark
`detection process. Different criteria may be applied to the
`watermark detection process for the verification of the
`watermarked portions, based on the desired degree of con-
`fidence for determining whether the appropriate watermark
`is present or absent, andthe desired degree of confidence for
`determining whether a modification has occurred.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`Theinvention is explained in further detail, and by way of
`example, with reference to the accompanying drawings
`wherein:
`
`FIG. 1 illustrates an example block diagram of a water-
`mark encoding system in accordance with this invention.
`FIG. 2 illustrates an example block diagram of a copy
`protection system in accordance withthis invention.
`FIG.3 illustrates an example flow diagram of an autho-
`rization test process in accordance with this invention.
`Throughout the drawings, the same reference numerals
`indicate similar or corresponding features or functions.
`
`DETAILED DESCRIPTION OF THE
`
`INVENTION
`
`U.S. Pat. No. 6,252,972 “METHOD AND ARRANGE-
`MENT FOR DETECTING A WATERMARKUSINGSTA-
`TISTICAL CHARACTERISTICS OF THE INFORMA-
`
`TION SIGNAL IN WHICH THE WATERMARK IS
`EMBEDDED”,
`issued Jun. 26, 2001 to Johan P. M. G.
`Linnartz, and incorporated by reference herein, teaches an
`encoding process wherein a particular binary pattern of +1
`and -] is added to each element of the content material. At
`the detector,
`the same binary pattern is applied to the
`received input signal
`to determine whether a sufficient
`correlation exists to decide that the received input contains
`
`this pattern. U.S. Pat. No. 6,208,735 “SECURE SPREAD
`SPECTRUM WATERMARKING FOR MULTIMEDIA
`
`DATA”, issued Mar. 27, 2001 to Ingemar J. Cox et al, and
`incorporated by reference herein teaches a watermarking
`
`
`
`
`
`me an
`
`30
`
`35
`
`40
`
`45
`
`50
`
`60
`
`65
`
`1
`COPY PROTECTION VIA REDUNDANT
`WATERMARK ENCODING
`
`BACKGROUNDOF THE INVENTION
`
`. Field of the Invention
`This inventionrelates to the field of data protection, and
`in particular to protecting data from illicit copying from a
`remote source,
`
`
`
`2. Description of Related Art
`The protection ofdata is becoming an increasingly impor-
`tant area of security. In manysituations, the authority to
`copy or otherwise process information is verified by evalu-
`ating the encoding of copy-protected material for particular
`characteristics. For example, on copy-protected material
`maycontain watermarksor other encodingsthat identify the
`material as being copy-protected, and also contains other
`encodings that identify whether this particular copyof the
`material is an authorized copy, and whetherit can be copied
`again. For example, an authorized copy of content material
`maycontain a robust watermark and a fragile watermark.
`The robust watermark is intendedto be irremovable from the
`encoding of the content material. Attempting to remove the
`watermark causes damage to the content material. The
`fragile watermark is intended to be damaged when the
`content material is illicitly copied. For example, common
`fragile watermarks are damaged if the content material is
`compressed or otherwise altered. In this manner, content
`naterial that is compressed in order to be efficiently com-
`nunicated via the Internet will be recetved with a robust
`
`watermark and a damaged fragile watermark. A content-
`processing device that is configured to enforce copyprotec-
`ion rights in this example will be configured to detect the
`presence of a robust watermark, and prevent the processing
`of the content material containing this robust watermark
`nless an appropriate fragile watermark is also present. The
`assumption being that compressed content represents an
`nauthorized transfer of copyrighted material.
`The design of a watermarking encoding process and
`corresponding watermark detection involves a tradeoff
`among conflicting requirements. An ideal watermark should
`be undetectable during a conventional rendering of the
`content material, yet easily detectable by the watermark
`detector. As the watermark’s detectability by the watermark
`detector increases, so too does its detectability during a
`conventional rendering; similarly, as the watermark’s unde-
`tectability during a convention rendering decreases, so too
`doesits undetectability by the watermark detector. Conven-
`tional watermarking processes are biased to assure that the
`watermarking process does not affect the quality of the
`rendering of the content material, often at the cost ofreduced
`detectability by a watermark detector. Thatis, the likelihood
`of a watermark detector producing an erroneous decoding of
`a watermark, or failing to detect the watermark,
`is not
`insubstantial.
`In the aforementioned use of both a robust watermark and
`
`fragile watermark, each watermarking process must be
`esigned within these conflicting tradeoff requirements, and
`ach watermarking process must be configured to have a
`ifferent susceptibility to damage. The robust watermark
`must be substantially undetectable by the conventional ren-
`dering process, yet also be robust enough to be recognizable
`after the watermarked material has been compressed and
`reformulated into a decompressed form. The fragile water-
`mark must also be substantially undetectable by the con-
`ventional rendering process, yet also fragile enough so that
`a reformulation of the material causes damageto the fragile
`
` a d e d
`
`
`
`

`

`US 7,133,534 B2
`
`4
`the number of properly detected
`encoder 120 such that
`watermarks can be used to distinguish between altered and
`unaltered content material.
`
`3
`technique wherein a spread spectrum encodingof the water-
`mark is applied to the content material, wherein the spread
`spectrum informationis particularlytargeted to the signifi-
`FIG. 2 illustrates an example block diagram of a security
`cant frequency components of the content material.
`system 200 that is configured to control the rendering of
`Because common watermark detection processes are not
`content material, based on the presence or absence of proper
`100% reliable, a fault in the detection process may be
`watermarks. The security system 200 includes a watermark
`interpreted by a security process as an erroneous watermark,
`tester 210 that is configured to detect a watermark and an
`and the rendering of the content material may be inappro-
`authorization tester 220 that is configured to control the
`priately terminated. That is, the content material may be
`rendering of the content material, via rendering system 240,
`authorized for rendering, and contain a proper watermark,
`based on the output of the watermark tester 210, and based
`but the fault
`in the detection process may indicate an
`onasetoftest criteria 250, via a gate 230. For the purposes
`improper watermark, or no watermark.
`of this invention, the term rendering is intended to include
`Tn accordance withthis invention, the watermark is redun-
`any subsequent processing,
`recording, modification, or
`dantly encoded such that the amount of redundancy deter-
`translation of the content material.
`mines the likelihood of the watermark being detected,
`In accordance with this invention, the authorization tester
`assuming a potentially faulty watermarking detection pro-
`220 is configured to determine whetherthe content material
`cess, and such that the number of proper detections of the
`watermark determines whether the material has been modi-
`is protected, based on whether any watermark is present in
`the content material. If the material is determined to be
`
`fied. In each of the above referenced encoding techniques,
`for example, the same pattern of +1 and -1 additions, or the
`same spread spectrum encoding is repeatedly applied to the
`content material.
`
`the redundantly water-
`During the detection process,
`marked content material is scanned until a corresponding
`+1/-1 pattern, or a corresponding spread spectrum encoding
`is detected. Assuming that the watermark detection process
`is potentially faulty,
`the number of times that the same
`pattern is encoded will determine the likelihood of the
`
`watermark beingdetected. If, for example, the watermark is
`only singly encoded, the likelihood of the watermark being
`detected will be (1-p), where p is the inherent probability of
`he watermark detector not properly detecting the water-
`nark. If the watermark is encoded twice, the likelihood of
`detection is (1-p); if the watermark is encodedthree times,
`he likelihood of detection is (1-p°); etc.
`If the watermarked content material is altered, the quality
`of the watermark decreases, and the inherent probability of
`he watermark detector not properly detecting the water-
`nark, using conventional watermark encoding and decoding
`echniques, increases. Defining this new inherent probability
`as q, the likelihood of a watermark detector not properly
`detecting a redundantly encoded watermark is expressed as
`1-q"), where n is the number of encodings of the same
`watermark.
`
`the parameter n is
`In accordance with this invention,
`selected to provide a very high likelihood of detection,
`regardless of whether the material is altered. In accordance
`with a second aspectofthis invention, the detection process
`includesa statistical procedure that further provides a con-
`rol over the likelihood of detecting altered watermarked
`content material, based on the probabilities of detection p
`and q, for unaltered and altered content material, respec-
`ively, discussed further below.
`FIG.1 illustrates an example block diagram of a water-
`nark encoding system 100 in accordance with this inven-
`ion. The encoding system 100 includes a redundancy con-
`roller 110 that controls a redundant watermark encoder 120.
`As noted above, any of a variety of watermark encoding
`echniques maybe included in the watermark encoder 120,
`provided that the technique allows for a repetition of the
`watermark within the same content material. In accordance
`with this invention, the redundancy controller 110 controls
`he redundant watermark encoder 120 suchthat the likeli-
`
`ood of detecting at least one copy of the watermark is high,
`even if the content material
`is altered. Additionally,
`the
`redundancy controller 110 controls the redundant watermark
`
`
`
`
`me an
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`
`protected, the authorization tester 220 is further configured
`to determine whether the watermarked content material has
`
`been altered, based on a measureof the qualityof a detected
`watermark.
`
`to remove a
`Consider, for example, an illicit attempt
`watermark from the watermarked content material
`that
`reduces the likelihood of a watermark being detected from
`a nominal 95% (1-p) to as low as 10% (1-q), and an
`encoding and detection process that is configured to detect
`the presence of the watermark at least 99% of the time.
`Using the equations presented above, in order to assure a
`99% detection rate with an increased non-detection rate of q,
`this equates to:
`(1-g”)<=0.01.
`
`In this example, with q=0.90, the number of redundant
`encodings, n, must be at least 42. Thus, the redundancy
`controller 110 of FIG. 1 would be configured to control the
`redundant watermark encoder 120 to produce at least 42
`redundant encodings of the watermark within the content
`material, and the authorization tester 220 of FIG. 2 would be
`configuredto determinethat the content material is protected
`if the watermark tester 210 detects at least one of these
`
`encodings. Because the watermark is redundantly encoded
`at least 42 times, at least one of these watermarksis likely
`to be detected, even if the likelihood of detecting each
`watermark is reduced to as low as 10%. Thus, the highly
`redundant encoding of the watermark allowsfor the detec-
`tion of the watermark even after a purposeful attempt to
`substantially reduce the likelihood of the watermark being
`detected.
`
`FIG.3 illustrates an example flow diagram of an autho-
`rization test process in accordance with this invention. At
`310, a count of the number of detected watermarks is
`initialized to zero. At 320, a watermark tester (210 in FIG.
`2) determines whether a watermarkis present in the content
`material. If a watermark is detected. at 330. the count is
`incremented, at 340. This process continues until termi-
`nated, at 350, typically by reaching the end of the content
`material, or the end of a predetermined segment of the
`content material that is expected to contain the watermarks.
`Upon termination, at 360, if no watermarks were detected,
`the content material is determined to be unprotected,at 370.
`In accordance with the secondaspectof this invention, the
`authorization tester 220 is further configured to determine
`whether the content material has been altered, based upon
`the numberof copies of the watermark that are detected. As
`noted above, due to limitations of watermark detection
`
`

`

`US 7,133,534 B2
`
`5
`processes, the likelihood of a watermarktester 210 failing to
`recognize a valid watermark is some non-zero percentage,p.
`Asalso noted above, a modification of content material has
`the effect of increasing this failure rate; hereinafter,
`this
`increased failure rate is termed “r”. Generally, this failure
`rate is lower than the aforementioned “gq”rate that is caused
`by anintentional attempt to remove the watermark, because
`it is generally an unintended secondaryeffect of a transfor-
`mation ofthe content material to, for example, a compressed
`form, such as MP3.
`If the content material is altered, the expected failure rate
`is “r”, and the numberofproperly detected watermarks from
`altered content material that contains “n” redundant water-
`marks is nX(1-r).
`If the content material is altered, the expected failure rate
`is“, and the numberofproperly detected watermarks from
`altered content material that contains “n” redundant water-
`
`
`
`narks is n*(1-r).
`In accordance with this second aspectof the invention, the
`umber of properly decoded watermarks is compared to
`each of these expected values, n*(1-p), nX(1-r), to deter-
`nine whetheror not the content material has been modified,
`at 380. Depending upon this comparison, a determinationis
`nade as to whether the sampled content material corre-
`sponds moreclosely to unaltered material, at 390, or altered
`naterial, at 395.
`To provide for a reliable determination, the number of
`redundant copies of the watermark,n, is selected to be large
`enoughto reliably distinguish between these expected val-
`es. For example, considera failurerate, p, of the watermark
`ester 210 is 0.10 given an unaltered content material, that
`rises to a rate, r, of 0.20 given an altered content material. If
`he numberof redundantcopies, n, is 10, then the expected
`value of properly decoded watermarks of unaltered content
`naterial will be 9, and the number of properly decoded
`watermarksof altered content material will be 8. Obviously,
`due to the random factors associated with detecting a
`watermark,
`it would be virtually impossible to reliably
`determine whether an observed numberof properly decoded
`watermarks was from a population whose expected value
`was 9, compared to a population whose expected value was
`8. That is, if in fact, 9 properly decoded watermarks were
`detected, one of ordinaryskill in the art would not be willing
`to conclude that these watermarks were not from an altered
`content material whose expected number of properly
`decoded watermarksis 8. In like manner, detecting only 8 of
`the 10 watermarks does not automatically lead to a conclu-
`sion that the content material has been altered. On the other
`and,
`if the number of redundant copies, n, were 100,
`leading to expected values of 90 and 80, for unaltered and
`altered material, respectively, it would be easier to distin-
`guish between the two.
`Preferably, conventionalstatistical techniques, such as the
`chi-square test, or any of a variety of binomial sampling
`ests, are used to determine an appropriate number of
`redundant copies, n,
`to provide for a reliable distinction
`between the failure rate caused bythe inherentfailure rate of
`he watermark detection process and the increased failure
`rate of the watermark detection process caused byan alter-
`ation of the content material. As in all statistical tests, two
`parameters, alpha andbeta, are used to qualify thereliability
`of the test. In this application, alpha is the likelihood of
`erroneously determining that unaltered content material has
`been altered, and beta is the likelihood of erroneously
`determining that altered content material has not been
`altered, Based on the estimated values of p, and r, and the
`particular test that is to be applied, the value of n can be
`
`
`
`
`
`6
`determined for providing not more than the specified alpha
`and beta likelihoods oferror. Alternatively stated, (1-alpha)
`and (1-beta) are the likelihoods of not making an erroneous
`decision, and are commonly termed the “confidence levels”
`associated with making a decision. In accordance with this
`invention, the numberof redundant copies of the watermark
`is determined so as to provide a desired level of confidence
`in distinguishing between altered and unaltered content
`material.
`
`the
`If the watermark detection process is such that
`absence of a proper watermark is detectable, such as a
`redundant watermarking process that applies a watermark at
`fixed time intervals, more powerfulstatistical tests may be
`employed, such as a runs-test or other sequential test. Of
`particular note, Wald’s Sequential Probability Ratio Test
`(SPRT)is particularly well suited for rapidlydistinguishing
`between samples drawn from two different populations. As
`each sample is evaluated,
`in this case as containing a
`detected or undetected watermark,
`the proportion of
`detected watermarks is compared to a ratio that is based on
`the expected values of each of the populations. If the
`proportion of detected watermarks substantially favors one
`population comparedto the other, the test is terminated, and
`the sample is determined to have been drawn from the
`substantially favored population.
`If the proportion of
`detected watermarks does not substantially favor one popu-
`lation or the other, another sample is drawn, and the test is
`repeated. As in conventionaltests, a total number ofpossible
`samples, n, can be determined suchthatthe test is concluded
`in favor ofone orthe other populations after the evaluation
`ofall the samples, n, with a given level of confidence in each
`decision, (1-alpha) and (1-beta). The advantage of the SPRT
`is that the test may be concluded sooner, with the samelevel
`of confidence, with fewer samples being evaluated.
`In a preferred embodimentofthis invention, the number
`of redundant watermarks, nl,
`required for providing a
`reliable detection of at least one copy of the watermarks in
`the presence of content material that has been intentional
`altered to provide a likelihood of detection of (1-q) is
`determined. And, the number of redundant watermarks, n2.
`required for reliably distinguishing between unaltered con-
`tent material having a likelihood of detection of (1-p) and
`altered content material having a likelihood of detection of
`(1-r) is determined. The larger ofthese two numbers, nl and
`n2, is used as the numberof redundant watermarks that are
`included in the protected content material so as to provide
`both a reliable detection of a watermark and also a reliable
`distinction between altered and unaltered watermarks.
`
`The foregoing merely illustrates the principles of the
`invention.It will thus be appreciated that those skilled in the
`art will be able to devise various arrangements which,
`although not explicitly described or shown herein, embody
`the principles of the invention and are thus within its spirit
`and scope. For example, the above examples do not assume
`that the watermark detector 210 will report the presence of
`a watermark when a watermark is not present. If such a
`possibility/probability exists, the aforementioned tests will
`be adjusted accordingly. In particular, for example, the test
`at 360 may allow a non-zero count as a threshold for
`determining whether the content materialis truly protected.
`In like manner, although the above examples assumethat
`each watermark is an identical copy of each other water-
`mark,
`the watermarks may vary, so as to facilitate, for
`example, fault isolation or other diagnostic function. These
`and other system configuration and optimization features
`
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`US 7,133,534 B2
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`7
`will be evidentto one of ordinary skill in the art in view of
`this disclosure, and are included within the spirit and scope
`of the following claims.
`The invention claimedis:
`1. A watermarking system comprising:
`a watermark encoder that
`is configured to encode a
`watermark upon a segmentof protected content mate-
`rial, and
`a redundancy controller, operably coupled to the water-
`mark encoder,that is configured to control the water-
`mark encoder to encode multiple watermarks upon the
`protected content material,
`the number of multiple
`watermarks being determined based on a probability of
`error or failure rate of the recieving system and a
`determination ofthe probability of the recieving system
`not detaching each of the multiple watermarks, wherein
`the redundancy controller determines a number of the
`multiple watermarks to encode upon the content mate-
`rial to facilitate detection of at least one of the multiple
`
`the
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`watermarks at a receiving system to allow that
`content material is protected.
`2. The watermarking system of claim 1, wherein the
`redundancy controller further determines the numberof the
`multiple watermarksto facilitate detection of a modification
`of the protected content material at the receiving system.
`3. The watermarking system of claim 1, wherein the
`number of multiple watermarks, n, satisfies the following
`equation:
`(1-g")<=k,
`wherein:
`q corresponds to a probability of not detecting each
`watermark in the content material, and
`k correspondsto a probability of error in determining that
`the content material is protected.
`4. A security system comprising:
`a watermark tester that is configured to detect a water-
`mark in select content material,
`an authorization tester, operably coupled to the watermark
`tester, that is configured to control the watermark tester
`to detect multiple watermarks in the content material,
`and
`
`
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`= 6
`
`25
`
`30
`
`35
`
`40
`
`55
`
`60
`
`65
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`8
`6. The security system of claim 5, wherein the sequential
`test includes a sequential probability ratio test.
`7. The security system of claim 4, further including:
`a rendering system that is configured to effect the render-
`ing of the content material.
`8. A method for determining access rights to content
`material, comprising:
`detecting one or more watermarks from amonga plurality
`of watermarksthat are encoded in the content material.
`maintaining a count of the one or more detected water-
`marks, and
`providing access to the content material based on the
`count, wherein
`providing access to the content material includes:
`comparing the count to a measurethat is based ona first
`and second expected values of counts,
`the first expected value corresponding to expected
`detections from the content material if the content
`material is unaltered, and
`the second expected value corresponding to expected
`detections from the content material if the content
`material is altered.
`9. The method of claim 8, wherein
`the measure is based ona statistical test, and
`the statistical test includes at least oneof:
`a chi-squaretest,
`a binomial test, and
`a sequential test.
`10. The method of claim 9, wherein
`the sequential test includes a sequential probability ratio
`test.
`
`11. The method of claim 8, further including:
`rendering the content material.
`12. A program stored on a processor readable medium for
`determining access rights to content material, comprising:
`a program portion configured to detect one or more
`watermarks from among a plurality of watermarksthat
`are encoded in the content material,
`a program portion configured to maintain a count of the
`one or more detected watermarks. and
`a program portion configured to provide access to the
`content material based on the countof the one or more
`detected watermarks, wherein
`the program portion configured to provide access to the
`content material includes:
`
`13. The program portion of claim 12, wherein
`the program portion configured to provide access to the
`content is configured to provide access to the content
`based on
`a result of a statistical test that is applied,
`based on the count, and
`the statistical test includes at least oneof:
`a chi-squaretest,
`a binomial test, and
`a sequential test.
`14. The program portion of claim 13, wherein
`the statistical test includes a sequential probability ratio
`test.
`
`a gate, operably coupled to the authorization tester, that is
`configured to control a rendering of the content mate-
`45
`a program portion configured to compare the countto
`rial, based on a detection of one or more of the
`a measurethat is based onafirst and second expected
`watermarks in the content material, wherein
`values of counts,
`the authorization tester is further configured to maintain a
`the first expected value corresponding to expected
`count of the multiple watermarks that are detected by
`detections from the content material if the content
`the watermarktester,
`naterial is unaltered, and
`the gate is further configured to control the rendering of
`the content material based on a comparisonof the count
`the second expected value corresponding to expected
`detections from the content material if the content
`of the multiple watermarks with a measure based on a
`naterial is altered.
`first and second expected values of counts,
`the first expected value corresponding to expected detec-
`tions from the content material if the content material
`is unaltered, and
`the second expected value corresponding to expected
`detections from the content material if the content
`material is altered.
`5. The security system of claim 4, wherein
`the gate is configured to control the rendering based on a
`result of a statistical test that is applied, based on the
`count, and
`the statistical test includes at least one of:
`a chi-squaretest,
`a binomialtest. and
`a sequential test.
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