WATERMARK SYSTEM

Abstract: A method for examining an electronic representation of an item for a watermark, the method including examining at least a first electronic representation of an item for a watermark in accordance with a first watermark definition, receiving a signal indicating that a second watermark definition is to be used for examining electronic representations, and examining at least a second electronic representation of an item for a watermark in accordance with the second watermark definition. Related apparatus and methods are also provided.

Description: WATERMARK SYSTEM FIELD OF THE INVENTION The present invention relates to electronic watermarking in general, and in particular to watermarking of electronic items which is resistant to removal of the watermark from the items. BACKGROUND OF THE INVENTION Electronic watermarking is well known in the art. Generally, in electronic watermarking a watermark signal of some kind is added to an electronic representation of an item, such as a recording or a broadcast signal. The added watermark signal known in the art may provide an indication of origin intended to provide traceability of a copied representation; and/or may indicate specific rights of a holder of the electronic representation, such as a right to use or play but no right to copy, or right to copy at reduced quality. Generally, implementation of such specific rights is termed "controlling access " , and the field of controlling access is also referred to as "conditional access " : these terms are used with the indicated meanings throughout the present specification and claims. Typically, in the case of specific rights associated with a watermark, conditional access is enforced by all legitimate devices which are operative to access, play back, or otherwise utilize the electronic representation. Added watermark signals may be added to a certain place in an electronic representation or may be "spread out " so that the watermark signal is found in many parts of the electronic representation. Added watermark signals may be easily perceived by one who plays back the representation, or may not be discernible upon normal playing of the representation. The art of adding a signal, including a watermark signal, to a medium in order to embed information which is not easily discernible upon normal examination or playback is generally termed "steganography' * . US Patent 5,606,609 to Houser et al describes an electronic document verification system and method in which a security object is embedded in an electronic document such as, for example, with an object linking and embedding (OLE) capability. Typically, the security object includes security information and an identifier for invoking the processing of the security information. US Patent 5,607,188 to Balms et al describes a technique of marking an optical disc for customized identification, m which a watermark is applied to a master disc, preferably by modifying the periodic diffraction grating effect created ■ . by encoded data the disc. US Patent 5,636,292 to Rhoads describes stcganography methods employing embedded calibration data on a carrier to be identified, the methods being intended to provide robustness despite degradation of the carrier and permeation of an imbedded signal throughout the earner 10 US Patent 5,659.726 to Sandford, II et al describes a method of embedding auxiliary information into a set of host data, in w hich pixels in the host data w hich are nearly identical and which have \ allies differing by less than an intrinsic noise \ aluc are manipulated and replaced with auxiliary data US Patent 5,664,018 to Leighton describes a w atermarking process i s in which each of a set of copies of a work has a slightly modified form of a baseline watermark placed within a critical region of the data, the slight variations not being perceptually visible and not interfering with the work US Patent 5,687,236 to Moskowitz et al describes a steganographic method and device for encoding and decoding information into a stream of 20 digitized samples, m which the information is contained in the samples, not prependcd or appended to the sample stream The method of Moskowit/ et al is used to establish ownership of copyrighted digital multimedia content and to provide a disincentive to piracy. Published PCT application WO 96/41468 describes a method and 25 apparatus for copyright protection of various recording media using a combination of a video finger print signal and an authenticating signature The authenticating signature is designed m such a way that it will not be transferred to illicit copies made on CD receivers. When a copy of a protected CD is played the absence of the authenticating signature causes the player to prohibit the disk from playing 30 normally. Published PCT application WO 97/13248 describes an electronic watermarking scheme which operates at a high level in the hierarchy of the (MPEG) source signal, thus attempting to ensure that the watermark is easily detectable but difficult to erase. Published PCT application WO 97/22206 describes a method for mark g a video and/or audio signal to identify, for example, that the signal is authentic and is not to be copied Published PCT application WO 97/26732 describes a method for stega-protection of computer code, encoding the code into a data resource with a digital w atermark, the digital watermark containing licensing information mterwox en with essential code resources Published PCT application WO 97/26733 describes a method for an encrypted digital watermark in which pseudo-random keys for encoding and decoding digital watermarks are generated and applied w ith human assistance Published PCT application WO 97'34391 describes a watermarking process intended to be resistant to collusion attacks Published PCT application WO 98/02864 describes optimization methods for insertion, protection and detection of digital watermarks based on individual chai acteπstics of a en digital stream Published PCT application WO 98/03014 describes a method for detecting a w atermark embedded m an information signal by correlating the information signal with a plurality of watermarks Eui opean Patent Application 0 651 554 A l describes a method and apparatus for addition and removal of digital watermarks in a hierarchical image storage and retrieval system, a digital watermark being added in a selected image resolution component and the means to remove it m an additional image component. Israel Patent Application 120174, assigned to the same assignee as the present application, describes a digital protection system m which encryption control messages (ECMs) in a first format are replaced with ECMs a second format Corresponding applications, all assigned to the same assignee as the present application, include" US Patent Application 09/014,791 ; published UK Patent Application 9725557.4, and published EPO Patent Application 98300596.8. The disclosures of all references mentioned above and throughout the present specification are hereby incorporated herein by reference. SUMMARY OF THE INVENTION The present invention seeks to provide improved apparatus and methods for watermarking and watermark examining and detection. Various different methods of producing and managing watermarks are described in the prior art Some prior art watermarking methods are intended to make illicit removal of watermarks difficult er, it is known that there are many methods for illicit watermark removal, and it is widely believed that any watermark known in the prior art can be removed if sufficient resources are devoted to removal of the watermark. The prior art does not provide a solution for providing continued protection after a watermark is successfully and illicitly removed. In a first embodiment of the present lm cntion. an electronic representation is provided with more than one w atermark Preferably each of the more than one watermarks is associated with a atermai k definition, which may define a location of the watermark m the electronic representation, a method by which the w atermark may be found, or any other appropriate parameter defining the watermark in a way sufficient to allow the watermark to be found A watermark examiner, operative to examine electronic representations for a watermark, preferably examines electronic repi esentations in accordance with a first watermark definition; preferably but not necessarily, m order to avoid illicit tampering, the watermark exammei docs not include any information, such as a second watermark definition, defining other watermarks beyond a first watermark. At some point, typically when it becomes known that knowledge as to how to remove the first watermark has become widespread, a signal is sent to the watermark examiner, the signal including a second watermark definition or information sufficient to derive a second watermark definition From that point on, the watermark examiner preferably examines in accordance with the second watermark definition and not the first watermark definition. In another preferred embodiment of the present invention, the watermark examiner, m response to a received signal as described above, may be operative to alter an electronic representation, typically an electronic representation comprising the first watermark, to comprise the second watermark. There is thus provided m accordance with a preferred embodiment of the present invention a method for examining an electronic representation of an item for a watermark, the method including examining at least a first electronic representation of an item for a watermark in accordance with a first watermark definition, mg a signal indicating that a second watermark definition is to be used for examining electronic representations, and examining at least a second electronic representation of an item for a watermai k in accordance w ith the second watermark definition. Further m accordance with a preferred embodiment of the present 10 ention the method also includes controlling access to at least the second electronic representation based, at least in part, on a result of the examining at least a second electronic representation step Still further accordance with a preferred embodiment of the present lm ention the first electronic representation and the second electronic i representation are identical. Additionally m accordance with a preferred embodiment of the present invention the signal includes a representation of the second watermark definition. Moreover m accordance with a preferred embodiment of the present 20 invention the method also includes retrieving the second watermark definition from a stoi age de\ ice m response to the received signal. Further m accordance with a preferred embodiment of the present invention the method also includes computing the second w atermark definition in response to the received signal. 25 Still further in accordance with a preferred embodiment of the present invention the first watermark definition and the second watermark definition each includes an indication of a location, within each electronic representation to be examined, at which a watermark, if present, is to be found. Additionally accordance with a preferred embodiment of the 30 present invention the first watermark definition and the second watermark definition each includes an indication of a watermarking method according to which each electronic representation to be examined is to be examined for a watermark. Moreover in accordance with a preferred embodiment of the present invention the signal includes authentication information for establishing that the signal originates from an authentic source, and the receiving step also includes s verifying the authentication information to determine w hether the authentication information is correct and rejecting the received signal if the authentication information is determined to be incorrect, thereby causing the fii st w atermark definition to continue to be used for examining if the authentication information is incorrect. 10 There is also provided accordance w ith another pi eferred embodiment of the present im ention a w atermark examiner for examining an electronic l epresentation of an item for a watermark, the apparatus including a watermark definition store operative to store a w atermai k definition, w atermark examination apparatus operatn ely associated w ith the w atermark definition store i s and opei ative to examine an electronic representation of an item for a watermark in accordance with the watermark definition stored m the w atermark definition store, and a watermark definition signal receiver operative to receive a signal indicating that a new watermark definition is to be used for examining electronic representations and to store the new watermark definition in the w atermark 20 definition store. Further m accordance with a preferred embodiment of the present invention the watermark definition includes an indication of a location, within each electronic representation to be examined, at which a watermark, if present, is to be found. 25 Still further m accordance with a preferred embodiment of the present invention the watermark definition includes an indication of a watermarking method according to which each electronic representation to be examined is to be examined for a watermark. Additionally m accordance with a preferred embodiment of the 30 present invention the signal includes a representation of the second watermark definition. Moreover m accordance with a preferred embodiment of the present invention the watermark examiner also includes a watermark storage memory for storing at least one watermark definition, and the watermark definition signal receiver is operative to retrieve the new watermark definition from the watermark storage memory in response to the received signal. 5 Further in accordance with a preferred embodiment of the present invention the watermark definition signal receiver is also operative to compute the second watermark definition in response to the received signal Still further accordance with a preferred embodiment of the present invention the signal includes authentication information for establishing 10 that the signal originates from an authentic source, and the w atermark definition signal receiver also includes signal verification apparatus operative to verify the authentication information to determine whether the authentication information is correct and to reject the received signal if the authentication information is determined to be incorrect, thereby causing the first watermark definition to i s continue to be used for examining if the authentication information is incorrect. There is also provided m accoi dance w ith another preferred embodiment of the present invention a method foi altering an electronic representation of an item having a watermark, the method including prov iding a first electronic representation of an item, the first electronic representation 20 including a first watermark, the first watermark corresponding to a first watermark definition, receiv ing a signal indicating that a second watermark definition is to be used, and altering the first electronic representation to include a second watermark corresponding to the second watermark definition Further m accordance with a preferred embodiment of the present 25 invention the altering step includes altering the first electronic representation to no longer include the first watermark. Still further m accordance with a preferred embodiment of the present invention the method also includes examining at least a second electronic representation for the second watermark. 30 Additionally m accordance with a preferred embodiment of the present invention the first electronic representation and the second electronic representation are identical. Moreover in accordance with a preferred embodiment of the present invention the method also includes controlling access to at least the second electronic representation based, at least in part, on a result of the examining at least a second electronic representation step. There is also provided m accordance with another preferred embodiment of the present invention a watermark alteration system for altering an electronic representation of an item having a watermark, the system including a watermark definition signal receiver for receiving a signal indicating that a second watermark definition is to be used, and watermark alteration apparatus foi altering a first electronic representation, the first electronic representation including a first watermark corresponding to a first watermark definition, to include a second watermark corresponding to the second w atermark definition Further m accordance with a preferred embodiment of the present invention the altering includes altering the first electronic representation to no longer include the first watermark. Still further in accordance with a preferred embodiment of the present inv ention the system also includes watermark examining apparatus for examining at least a second electronic representation for the second w atermark Additionally in accordance with a preferred embodiment of the present invention the first electronic representation and the second electronic representation are identical Moreover in accordance with a preferred embodiment of the present invention the watermark examining apparatus is also operative to control access to at least the second electronic representation based, at least m part, on a result of the examining of the at least a second electronic representation. There is also provided in accordance with another preferred embodiment of the present invention a signal for indicating to a watermark examiner that a second watermark definition is to be used place of a first watermark definition for examining electronic representations, the signal including a representation of a second watermark definition. Further m accordance with a preferred embodiment of the present invention the signal also includes authentication information for establishing that the signal originates from an authentic source. BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be understood and appreciated more fully from the following detailed description, taken m conjunction with the drawings which: 5 Fig. 1 is a simplified partly pictorial, partly block diagram illustration of a watermark examiner constructed and operative in accordance with a preferred embodiment of the present invention; Fig. 2 is a simplified flowchart illustration of a preferred method of operation of the watermark examiner of Fig. 1 ; 10 Fig 3 A is a simplified partly pictorial, partly block diagram illustration of a watermark alteration system constructed and operative in accordance ith an alternative preferred embodiment of the present invention; Fig. 3B is a simplified partly pictorial, partly block diagram illustration of the system of Fig 3 A, useful in understanding the operation thereof, l s and Fig 4 is a simplified flowchart illustration of a preferred method of operation of the watermark alteration system of Fig. 3 A DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT Reference is now made to Fig. 1 which is a simplified partly pictorial, partly block diagram illustration of a watermark examiner constructed and operative in accordance with a preferred embodiment of the present invention. 5 The present invention deals with watermarks in an electronic representation of an item. The terms '"electronic representation of an item " and "electronic representation " are used interchangeabh herein to denote am appropriate electronic representation capable of being watermarked w ith more than one w atermark, examples of such electronic representations including w ithout 10 limitation, any appropriate electronic signal, including a signal internal to an electronic device, a signal sent or transmitted by an electronic device, and a broadcast signal; any appropriate electronic recording, such as a CD. a CD-ROM, a digital ideo disk (DVD), a digital tape recording, oi any other electronic recording; an electronic representation inside a computei or stored on a computer i s readable medium, a digitization of a non-electronic representation of an item; and any other appropriate electronic representation The apparatus of Fig. 1 preferably comprises a watermark examiner 90, w ith which an electronic representation comprising a disk 100 is operatively associated In the embodiment of Fig 1 the disk 100, t\ pically comprising a pre- 20 recorded disk such as a CD or a DVD, is shown bv w ay of example of an electronic repi esentation only, it being appreciated that persons skilled in the art would be able to appropriately modify the apparatus of Fig 1 to be operative with other types of electronic representation such as those described above. It is particularly appreciated that the present invention is not limited to a disk or to any 25 similar medium, but is applicable generally to electronic representations as mentioned above. It is further appreciated that, in the case of a disk such as the disk 100, either a pre-recorded and non-alterable disk or an alterable and/or rewritable disk may be used. The disk 100 preferably comprises at least two watermarks, shown 30 in Fig. 1 as a first watermark 1 10 and a second watermark 120. It is appreciated, as is well known the art of watermarking, that a watermark may be" local to a particular part of an electronic representation or spread over most or all of an electronic representation; visible or otherw ise sensible to a person viewing the electronic representation or a playback of the electronic representation, or invisible and not otherwise sensible, and may, generally, have a wide variety of different attributes similar to those which are known the prior art. The first watermark 1 10 and the second watermark 120 are shown as being v isible and locali/cd by way of example only and for simplicity of depiction and description, it being appreciated that used of non-local and/or invisible watermai ks may be preferred. The terms "view " and "playback " , in their \ arious grammatical forms, are used throughout the present specification and claims to denote iewing, hearing, or otherwise experiencing with the senses a playback or other instantiation in palpable form of an electronic representation. Without limiting the genei ality of the foregoing and bv w a> of example onh , "\ iew " mav describe w atching a television screen, listening to music, or reading a printed document, while "plav back " mav refer to audio plav back. \ isual play back, and/or printing of an electronic representation. In addition to conventional components generally found in pπor art playback device and which may be comprised in or operativ cly associated w ith the watermark examiner 90 and operative to provide disk playback functionality, as is well known m the art, the watermark examiner 90 preferably comprises watermark examination apparatus 130 The watermark examination apparatus 130 is preferably operative to examine the disk 100 for a watermark m accordance w ith a watermark definition The watermark examination apparatus 130 may be operative, based on a watermark which is or is not found, to msti uct other components of the watermark examiner 90, such as conventional components or other components (not shown) of the watermark examiner 90, to limit or otherwise modify playback of the disk 100, or to provide conditional access thereto, as is well known in the art. The watermark examiner 90 also preferably comprises a watermark definition store 140, which may comprise any appropriate storage and retrieval apparatus, such as a memory, preferably comprising an appropriate non-volatile memory such as an NVRAM or an EEPROM. The watermark definition store 140 is preferably operative to store a watermark definition. The watermark definition store 140 is preferably operatively associated with the watermark examination apparatus 130 and operative to transmit a stored watermark definition stored the watermark definition store 140 to the watermark examination apparatus 130 It is appreciated that, m an alternative embodiment of the present invention, the watermaik definition store 140 may be comprised in the watermark examination apparatus 130. The watermark examiner 90 also preferably comprises a watermark definition signal receiver 150, operatively associated with the watermark definition store 140 The watermark definition signal receiver 150 may comprise any appropriate receiver circuitry, as is well known m the art, operativ e to receive a signal comprising a new watermark definition, exti act therefrom the new watermark definition, and transmit the new watermark definition to the watermark definition store 140. The signal received by the watermark definition signal receiver 150 is generally sent by a watermark definition center (not shown), which may be local to the watermark examiner 90 or remote therefrom. The signal may be sent to the watermark definition signal receiver 150 using any appropriate signal transmission means such as, for example: by wired transmission; by w ireless transmission, by transmission via a network, such as the Internet or any other appropriate network; multiplexed together with other transmissions, including, in an alternative embodiment of the present invention, a transmission of the electronic representation of an item; as a non-multiplexed transmission, or otherwise, as is well known m the art of data transmission The operation of the system of Fig. 1 is now briefly described. When the disk 100 is played back the watermark examination apparatus 130 preferably examines the stream of played back electronic information thereby produced, either continuously or at defined intervals or at defined locations the stream of played back electronic information as is well known m the art, to determine whether a watermark is present and, preferably, to determine the contents of the watermark The watermark examination apparatus 130 preferably takes action based on the watermark, as is well known m the art and as is described above. Alternatively, the watermark examination apparatus may play back a specific portion of the disk 100 order to determine whether a watermark is present. The watermark examination apparatus 130 preferably examines the played back electronic information, as described above, in accordance with a first watermark definition stored in and supplied by the watermark definition store 140 By way of example, the first watermark definition supplied by the watermark definition store 140 may cause the watermark examination apparatus 130 to examine the disk 100 or the played back electronic information as described above for the first watermark 1 10. The watermark definition store: may hav e been prev iously supplied w ith the first watermark definition substantiallv as described below w ith respect to a second watermark definition, may have been preloaded w ith the first w atermark definition such as, foi example, by preloading during manufacture of the watermark examiner 90, or may hav e been supplied w ith the first w atermark definition in any other appropriate mannci Generally, a new watermark signal will be sent to the w atermark definition signal receiver 150 from a watermark definition center (not show n) upon a determination that it is appropriate to use a new w atermark definition, for example, and without limiting the generality of the foregoing, it may be deemed appropriate to use a new watermark definition when it becomes know n that knowledge as to how to remove the first watermark has become widespread A new watermark signal may comprise a new watermark definition, suitable for use directly by components such as the watermark definition store 140 and the watermark examination apparatus 130 of the watermark examiner 90 Alternatively, a new watermark signal may comprise instructions sufficient to allow an appropriate component of the watermark examiner 90, such as, for example, the watermark definition signal receiver 150, to derive a new watermark definition from the instructions comprised m the new watermark signal. By way of example only and without limiting the generality of the foregoing, the instructions might comprise n binary decisions which, when combined, may be used to derive a new watermark definition based on pre-knowledge of the n binary questions to which the decisions refer. Alternatively and by way of further example only, the instructions might comprise a key for decrypting a new watermark definition already stored m encrypted form m the watermark examiner 90, such as in the watermark definition signal receiver 150. When the watermark definition signal receiver 150 receives a new watermark signal, the watermark definition signal receiver 1 50 preferably determines the correctness of the received signal using any appropriate method or methods well known in the art. Without limiting the generality of the foregoing, a new w atermark signal may be digitally signed, as is well known in the art, and only a properly signed watermark signal may be accepted by the w atermark definition signal receiver 150. A digital signing method, or alternatively any similar appropriate method, is believed to be preferred in order to prevent sending of a fi audulent new watermark signal, which could possibly cause the watermark examiner 90 to cease effective examination of the disk 1 0 foi watermarks The new watermark definition signal comprises, as described abov e. a new w atermark definition or an effective substitute therefor in the form of appropriate instructions The new watermark definition, also termed herein a second watermark definition, is preferably stored in the atermark definition store 140 by the w atermark definition signal receiver 150 Thereafter, by normal operation of the watermark examination apparatus 130 as described abov e, the watermark examination apparatus 130 uses the second watermark definition to examine, foi example, the second watermark 120. Thus, upon receipt of a new w atermai k signal the w atermark examiner 90 ceases to examine for the first watermark 1 1 0 and begins to examine for the second watermark 120. It will be appreciated that continued protection is provided by the embodiment of Fig 1 even in a case where the first watermark 1 10 has been successfully and illicitly removed. In this w ay, a solution is provided to a significant drawback m the prior art, in that the prior art does not provide a solution for providing continued protection after a watermark is successfully and illicitly removed. Reference is now made to Fig. 2, which is a simplified flowchart illustration of a preferred method of operation of the watermark examiner of Fig. 1 The method of Fig. 2 preferably comprises the following steps: At least a first electronic representation of an item, typically but not necessarily comprising a plurality of electronic representations of one or more items, is examined for a watermark in accordance with a first watermark definition (step 160). A signal is received, the signal indicating that a second watermark 5 definition is to be used for examining electronic representations (step 170) It is appreciated that the signal of step 170 may be as described abov e with refei ence to Fig. 1 or, alternatively, may be any appropriate signal indicating that a second watermark definition is to be used. After receipt of the signal, at least a second electronic representation of an item, typically but not necessarily compi ismg a 10 plurality of electronic representations of one or more items, is examined for a watermark accordance with the second w atermark definition (step 1 80) It is appreciated that the second electronic representation and the first electronic representation may be identical. Reference is now made to Fig 3A, which is a simplified partly i s pictorial, partly block diagram illustration of a watermark alteration system constructed and operativ e in accordance with an alternativ e preferred embodiment of the present invention The apparatus of Fig 3A is pi eferably similai to the apparatus of Fig. 1 , except as described below However, it is appreciated, as described more fully below, that certain depicted components of the appai atus of 20 Fig. 3A which arc common to the apparatus of Fig 1 may be optional in the apparatus of Fig. 3 A The apparatus of Fig. 3A preferably also comprises watermark alteration apparatus 190, operatively associated with the watermark definition signal receiver 150 and typically operative to receive theicfrom the new watermark 25 definition. The watermark alteration apparatus 190 is also preferably in operative communication with the disk 100, either directly or through other components of the apparatus of Fig. 3 A such as, for example, conventional components. The watermark alteration apparatus 190 typically is implemented in special purpose hardware or a combination of hardware and software The 30 watermark alteration apparatus 190 is operative, given a first watermark definition and a second watermark definition, as the new watermark definition is also termed herein, to add a second watermark (not shown m Fig. 3A) to the disk 100, the second watermark being m accordance with the second watermark definition. It is thus appreciated that, the embodiment of Fig. 3A, the disk 100 preferably comprises an appropriate disk which is rewritable, erasable and wπteable, or otherwise modifiable. s It is appreciated that, in another alternative embodiment of the present invention, the watermark definition store 140 and the watermark examination apparatus 130 of Fig. 3A are optional. The operation of the apparatus of Fig. 3A is now briefly described. Except as described below, the operation of the apparatus of Fig 3A may be 0 similai to the operation of the apparatus of Fig. 1 . described above Upon receipt of a new watermark signal bv the watermark definition signal receiv er 1 50, and upon receipt of the new watermark definition by the watermark alteration apparatus 190, the watermark alteration apparatus 190 is operative to add a new watermark, as described above, to the disk 1 0 Reference 5 is now additionally made to Fig. 3B, which is a simplified partly pictorial, partly block diagram illustration of the system of Fig 3A, useful in understanding the operation thereof In Fig. 3B a second watermark 120 is shown, the first watermark 1 10 hav ing been removed from the disk 100. Typically the first watermark 1 10 is 0 removed by the watermark alteration apparatus 190 when the second w atermark 120 is added, but alternatively the first watermark 1 1 0 need not be removed Preferably, in a case where the first watermark 1 10 includes information such as conditional access information, similar information is included m the second watermark 120. 5 Preferably, m adding the second watermark 120 the watermark alteration apparatus 190 uses any suitable method, suitable to the type of disk 100 and the type of the second watermark 120 and possibly also of the first watermark 1 10. By way of example, and without limiting the generality of the foregoing, for a type of watermark which is spread out over all or most of the disk 100 the 0 watermark alteration apparatus 190 may read, analyze, and rewrite all or most of the contents of the disk 100; for a localized type of watermark, the watermark alteration apparatus 190 may read, analyze, and rewrite only a portion of the contents of the disk 100. Persons skilled m the art will appreciate that an appropriate method of operation should be chosen accordingly, and that preferably the watermark alteration apparatus 190 is capable of implementing more than one such method of operation. Reference is now made to Fig. 4, which is a simplified flowchart illustration of a preferred method of operation of the w atermark alteration system of Fig. 3 A. The method of Fig. 4 preferably includes the following steps: A first electronic representation of an item is prov ided; the first electronic representation includes a first watermark corresponding to a first watermark definition (step 200). When a signal is receiv ed indicating that a second watermark definition is to be used (step 2 10), the first electronic representation is altered to include a second w atermark corresponding to the second watermark definition (step 220). As described above with reference to Fig 3 A, the first w atermark may optionally be removed as part of step 220 As also described abov e with reference to Fig. 3 A, the method of Fig. 4 may be earned out m apparatus such as that described as another alternative embodiment of the pi cscnt invention, in which elements 130 and 140 of Fig. 3 A are typically not present. It is appreciated that various features of the inv ention which are, for clarity, described in the contexts of separate embodiments may also be prov ided in combination in a single embodiment. Conversely, v arious features of the invention which are, for brevity, described in the context of a single embodiment may also be provided separately or m any suitable subcombination. It will be appreciated by persons skilled in the art that the present invention is not limited by what has been particularly shown and described here above. Rather the scope of the invention is defined only by the claims which follow:

Claims: What is claimed is. CLAIMS 1. A method for examining an electronic representation of an item for a watermark, the method comprising: examining at least a first electronic representation of an item for a watermark in accordance with a first watermark definition; receiving a signal indicating that a second atermark definition is to be used for examining electronic representations; and examining at least a second electronic representation of an item for a watermark in accordance with the second w atermark definition. 2. A method according to claim 1 and also comprising: controlling access to at least the second electronic representation based, at least in part, on a result of the examining at least a second electronic representation step. 3. A method according to claim 1 or claim 2 and wherein the first electronic representation and the second electronic representation arc identical. 4. A method according to any of the above claims and wherein the signal comprises a representation of the second w atermark definition. 5. A method according to any of the above claims and also comprising: retrieving the second watermark definition from a storage device m response to the received signal. 6. A method according to any of the above claims and also comprising computing the second watermark definition response to the received signal. 7. A method according to any of the above claims and wherein the first watermark definition and the second watermark definition each comprises an indication of a location, within each electronic representation to be examined, at which a watermark, if present, is to be found. 8. A method according to any of the above claims and wherein the first watermark definition and the second watermark definition each comprises an s indication of a watermarking method according to which each electronic representation to be examined is to be examined for a watermark. 9. A method according to any of the abov e claims and wherein the signal comprises authentication information for establishing that the signal 0 originates from an authentic source, and the receiving step also includes. verifying the authentication information to determine whether the authentication information is correct and rejecting the received signal if the authentication mfomiation is determined to be incoirect. thereby causing the first 5 watermark definition to continue to be used for examining if the authentication information is incorrect. 10 A watermark examiner for examining an electronic representation of an item for a watermark, the examiner comprising 0 a watermark definition store operative to store a watermark definition; watermark examination apparatus operativ ely associated w ith the watermark definition store and operative to examine an electronic representation of an item for a watermark in accordance with the watermark definition stored in the 5 watermark definition store; and a watermark definition signal receiver operative to receive a signal indicating that a new watermark definition is to be used for examining electronic representations and to store the new watermark definition in the watermark definition store. 0 1 1. A watermark examiner according to claim 10 and wherein the watermark definition comprises an indication of a location, within each electronic representation to be examined, at which a watermark, if present, is to be found. 12. A watermark examiner according to eithei claim 10 or claim 1 1 and wherein the watermark definition comprises an indication of a watermarking method according to which each electronic representation to be examined is to be examined for a watermark 13. A watermark examiner according to am of claims 10 - 12 and wherein the signal comprises a representation of the second w atermark definition 14. A w atermark examiner according to am of claims 10 - 12 and w herein the w atermark examiner also comprises a w atcπnai k storage memory for storing at least one watermark definition, and the watermark definition signal receiver is operative to retriev e the new w atermark definition from the watemiark storage memory m response to the recei ed smnal. 15. A watermark examiner according to am of claims 10 - 14 and wherein the watermark definition signal receiver is also operativ e to compute the second w atermark definition in response to the received signal 16. A watermark examiner according to am of claims 10 - 14 and wherein the signal comprises authentication information for establishing that the signal originates from an authentic source, and the watermark definition signal receiver also includes. signal verification apparatus operative to verify the authentication information to determine whether the authentication information is correct and to reject the received signal if the authentication information is determined to be incorrect, thereby causing the first watermark definition to continue to be used for examining if the authentication information is incorrect. 17 A method for altering an electronic representation of an item having a watermark, the method comprising: providing a first electronic representation of an item, the first electronic representation comprising a first watermark, the first watermark corresponding to a first watermark definition; receiving a signal indicating that a second w atermark definition is to be used; and altering the first electronic representation to comprise a second watermark corresponding to the second watermark definition. 18 A method according to claim 17 and w herein said altering step comprises: altering the first electronic representation to no longer comprise the first watermark s 19. A method according to claim 17 or claim 1 8 and also comprising: examining at least a second electronic representation for the second watermark 20. A method according to claim 19 and w herein the first electronic 0 representation and the second electronic representation ai c identical 21 A method according to claim 19 or claim 20 and also comprising: controlling access to at least the second electronic representation based, at least in part, on a result of the examining at least a second electronic 5 representation step. 22. A watermark alteration system for altering an electronic representation of an item having a watemiark, the system comprising" a watermark definition signal receiver for receiving a signal 0 indicating that a second watermark definition is to be used; and watermark alteration apparatus for altering a first electronic representation, the first electronic representation comprising a first watermark corresponding to a first watermark definition, to comprise a second watermark corresponding to the second watemiark definition. 23. A system according to claim 22 and wherein said altering s comprises" altering the first electronic representation to no longer comprise the first watermark. 24. A system according to claim 22 or claim 23 and also comprising 0 watermark examining apparatus for examining at least a second electronic representation for the second watermark 25. A system according to claim 24 and wherein the first electronic representation and the second electronic representation ai e identical 5 26. A system according to claim 24 or claim 25 and wherein the watermark examining apparatus is also operative to control access to at least the second electronic representation based, at least in part, on a result of the examining of the at least a second electronic representation. 0 27. A signal for indicating to a watermark examiner that a second watermark definition is to be used in place of a first watermark definition for examining electronic representations, the signal comprising: a representation of a second watermark definition. 5 28. A signal according to claim 27 and also comprising: authentication information for establishing that the signal originates from an authentic source.

Inventors: TSURIA YOSSEF, TSURIA, YOSSEF
Applicants: NDS LTD, TSURIA YOSSEF, NDS LIMITED, TSURIA, YOSSEF
Application year: 2000
Main classification: H04N5
IPC codes: G06T1, G11B20, H04N5, H04N7