Abstract:
A two level cross-correlation based system for watermarking continuous digital media at the system application level. It is a post-compression process for watermarking where no a priori knowledge of the underlying compression algorithm is required. Per each compressed media frame, a current unique digital signature is generated based on the data from the current compressed frame plus the digital signature that has been previously generated. The signature thus generated is then used in conjunction with the next compressed frame to generate the next unique digital signature. All digital signatures are correlated according to the above process until a “reset” signal is issued. A new chain of correlated digital signatures is produced by the system with a pre-determined initial signature.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is a continuation of U.S. Ser. No. 11/262,006, entitled “Two Level Cross-Correlation Based System for Watermarking Continuous Digital Media” filed Oct. 28, 2005, now U.S. Pat. No. 7,715,588. This invention is related to U.S. Ser. No. 11/260,906, entitled “Correlation-Based System for Watermarking Continuous Digital Media”, filed Oct. 28, 2005, now U.S. Pat. No. 7,715,587, by co-applicants, Pan et al, and assigned to the present assignee and is also related to the co-filed patent application, U.S. Ser. No. 12/775,845. U.S. Ser. No. 11/260,906 is incorporated by reference herein in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to multimedia authentication and more particularly to a two level cross-correlation based system for watermarking continuous digital media. The primary area for the application of the present invention is the content authentication and ownership identification for continuous digital media that are prone to active attacks such as unauthorized removal and unauthorized embedding. Furthermore, to protect the watermarks from being easily tampered or detected by unauthorized personnel, a method of “two level cross-correlation” is thus introduced while watermarks are being created. 
     2. Description of the Related Art 
     Watermarking has been widely used for the applications of multimedia authentication and copyright protection. Video watermarking, in particular, is unique to other types of media watermarking in that it deals primarily with real-time continuous bitstreams. Many prior art references have focused on watermarking at the video compression level. See for example, D. Simitopoulos, N. Zissis, P. Georgiadis, V. Emmanouilidis, and M. G. Strintzis, “ Encryption and watermarking for the secure distribution of copyrighted MPEG video on DVD,”  Multimedia Systems  9 : pp 217-227, 2003; N. J. Mathai, D. Kundur, and A. Sheikholeslami, “ Hardware Implementation Perspectives of Digital Video Watermarking Algorithms,”  IEEE Transactions on Digital Signal Processing, Vol. 51, No. 4, April 2003; S. W. Kim and S. Suthaharan, “ An Entropy Masking Model for Multimedia Content Watermarking ,” Proceedings of the 37 th  Hawaii International Conference on System Sciences, 2004; W. Zhu, Z. Xiong, and Y. Q. Zhang, “ Multiresolution Watermarking for Images and Video ,” IEEE Transactions on Circuits and Systems for Video Technology, Vol. 9, No. 4, June 1999; M. Maes, T. Kalker, J-P. Linnartz, J. Talstra, G. Depovere, and J. Haitsma, “ Digital Watermarking for DVD Video Copy Protection ,” IEEE Sigmal Processing Magazine, September 2000. Although these methods generally produce good protection by taking into consideration the information contents of the underlying video, they tend to consume extra processing power that can otherwise be used to improve the performance of the encoder and/or reduce the latencies caused by time-critical tasks. 
     As will be disclosed below, the present invention provides for an efficient implementation of video watermarking at the system level and yet produces good protection and authentication on the recorded videos. 
     SUMMARY OF THE INVENTION 
     In a broad aspect, the present invention is a two level cross-correlation based system for watermarking continuous digital media. The two level cross-correlation based system includes an application control module (ACM) including a graphical user interface (GUI), for i) logically AND&#39;ing a predetermined frame correlation vector (FCV) and a predetermined frame mask vector (FMV) to generate a frame switch vector (FSV) that provides controls to an external frame switching means; and, ii) logically AND&#39;ing a predetermined signature correlation vector (SCV) and a predetermined signature mask vector (SMV) to generate a signature switch vector (SSV) that provides controls to an external signature switching means. The ACM also provides: i) an enable/disable control signal in response to a command by the user via the GUI; and, ii) a reset signal. A media encoder receives uncompressed media data from a media source and provides compressed media frames (F j ). A file system captures the compressed media data from the media encoder. A software retrieval module (SRM) retrieves the compressed media frames (F j ) from the file system. A first signature buffer buffers a previously generated signature (S j−1 ). A second signature buffer is operatively connected to the first signature buffer for buffering a currently generated unique digital signature (S j ), wherein a transition from the second signature buffer to the first signature buffer occurs when a transition takes place from one frame to the next. A third signature buffer stores a predefined initial signature (S 0 ). A 2:1 multiplexer (MUX) receives an input from the first signature buffer (S j−1 ), and another input from the third signature buffer (S 0 ). The reset signal from the ACM is a select control input signal to the 2:1 MUX, wherein one of the two inputs (S j−1 ) and (S 0 ) is selected as the output from the 2:1 MUX depending on the logic value of the reset signal. A frame switching means is operatively connected to the SRM and the FSV of the ACM for controlling the flow of the compressed frames F j  from the SRM. A signature switching means is operatively connected to the 2:1 MUX and the SSV of the ACM for controlling the flow of the output from the 2:1 MUX. A signature generator is operatively connected to the frame switching means, to the signature switching means, and to the ACM, for generating a unique digital signature (S j ) based on i) the F j , if the frame switching means is “on”, ii) the output from said 2:1 MUX, if the signature switching means is “on”, and iii) the status of said enable/disable control signal. The signature generator provides the S j  to the second signature buffer if the enable/disable control signal is set to “enable”. The signature generator provides no signature if the enable/disable control signal is set to “disable”. If both of the frame switching means and the signature switching means are “off”, then a “null signature” is generated and the null signature is provided to the second signature buffer if the enable/disable control signal is set to “enable”. The signature generator provides no signature if the enable/disable control signal is set to “disable”. An encryptor receives the unique digital signature (S j ) and encrypts the unique digital signature if the enable/disable control signal is set to “enable” and then stores the encrypted unique digital signature (E j ) to the file system. The signature generator provides no signature to the encryptor if the enable/disable control signal is set to “disable”. 
     Use of the present invention has several advantages over the prior art. (1) The present watermarking method applies to continuous digital media data such as video or audio rather than still images. (2) The method can be applied directly to the compressed media data. Therefore, the amount of data to be processed is tremendously reduced. (3) No knowledge of the underlying media compression algorithm is required in the present method; hence the computational complexity is greatly reduced. This is contrary to many prior art systems where the watermarking techniques are built on top of the compression algorithms. (4) The present method applies directly to the compressed media frames with variable lengths rather than to the uncompressed frames with a common fixed length. This increases the difficulty of tampering without being detected. (5) A unique digital signature is to be generated per each frame based on the input data from the current compressed frame and the previous signature. No specific digital signature generation algorithm is preferred, i.e., any digital signature generation process can be employed. The signature thus generated is “correlated” with the previous frame via the previously generated signature. Furthermore, the “correlation” is crossly created via a two level control process in which the frame and the signature involved in the current signature generation process are determined through a frame correlation vector and a signature correlation vector, respectively. This makes the piracy of the original media contents extremely difficult and the detection of the piracy very easy to implement, for if any frame has been modified, all the signatures corresponding to that frame and beyond will be wrong. (6) All the digital signatures are “correlatively” generated based on the predefined frame and signature correlation vectors until it is instructed to “reset” to the initial signature or change the correlations defined in the frame and the signature correlation vectors to begin a new correlated signature generation process. The control of the “reset” and the change of the two correlation vectors further create the dynamics to the pattern of the signatures being generated, which makes the media content even more difficult from being tampered with. (7) The overall watermarking operation of the present invention can be easily implemented at the Application level, which requires very minimum system resource and therefore can be easily integrated with the entire system. (8) A fast “False Detection” program can be easily written to detect and identify which frame or frames have been tampered without the need of decoding the entire media content—a tremendous saving in time can be achieved. 
     The watermarking technique of the present invention is commonly applied to digital media such as video and audio. However, the same method is applicable to any digital media that are continuous in nature. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a flow diagram illustrating the two level cross-correlation based system for watermarking continuous digital media of the present invention. 
         FIG. 2  is a flow diagram illustrating an example of the operation of the present invention. 
         FIGS. 3A-3I  illustrate the  FIG. 2  example with step-by-step details. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings and the characters of reference marked thereon,  FIG. 1  illustrates a preferred embodiment of the two level cross-correlation based system for watermarking continuous digital media of the present invention, designated generally as  10 . This two level cross-correlation based system  10  includes an application control module (ACM)  12  that includes a graphical user interface (GUI)  14 , a frame correlation vector (FCV)  9  of length K (K bits, labeled from 0 to K−1), a frame mask vector (FMV)  11  of length K, a logical AND operator  13 , a frame switch vector (FSV)  15  of length K, a signature correlation vector (SCV)  1  of length L (L bits, labeled from 0 to L−1), a signature mask vector (SMV)  3  of length L, a logical AND operator  5 , and a signature switch vector (SSV)  7  of length L. The FCV  9  defines a correlation, or a selection criterion, among frames. For example, the j-th compressed Frame F j  will be selected if FCV[k]=1, where j=k mod K. F j  will be de-selected if FCV[k]=0. The FMV  11  defines a frame mask which, when logically ANDed with FCV  9  via the AND operator  13 , provides a binary decision stored in the FSV  15  that determines whether a frame will eventually be selected to join the current signature generation process. For example, F j  will be selected to participate in the j-th signature generation process for the digital signature S j+1  if FSV[k]=1, where j=k mod K. F j  will be skipped if FSV[k]=0. Likewise, The SCV  1  defines a correlation, or a selection criterion, among signatures. For example, the j-th signature S j  will be selected if SCV[n]=1, where j=n mod L. S j  will be de-selected if SCV[n]=0. The SMV  3  defines a signature mask which, when logically ANDed with SCV  1  via the AND operator  5 , provides a binary decision stored in the SSV  7  that determines whether a signature will eventually be selected to join the current signature generation process. For example, S j  will be selected to participate in the j-th signature generation process for the digital signature S j+1  if SSV[n]=1, where n=j mod L. S j  will skipped if SSV[k]=0. The ACM provides the serially On/Off control outputs  39  from FSV  15  rotationally (starting from bit number  0 ) and the serially On/Off control outputs  43  from SSV  7  rotationally (starting from bit number  0 ). The ACM  12  also provides an enable/disable control signal  16  and a reset signal  18  in response to a command by the user via the GUI  14  and file system information  20 , respectively. The ACM  12  may be embodied as part of application software which allows users to provide control and configuration to a typical stationary Digital Video Recording (DVR) system or completely embedded control software in a mobile DVR system which is generally installed and operated in a mobile vehicle such as a police car or a bus. 
     A file system  22  captures compressed continuous media data  23  from the Media Encoder (ME)  25 . The compressed continuous media data is generally embodied in forms of media frames (F j ). The ME  25  receives the uncompressed media data  29  from a media source such as a camera  27 . The uncompressed media data  29  may be audio/video data, solely video data or solely audio data. Furthermore, it may be in analog form or digital form. If it is in analog form the media encoder  25  typically provides a conversion from analog to digital. Similarly, the compressed media data may be audio/video data, solely video data or solely audio data. 
     A software retrieval module (SRM)  26  retrieves the compressed media frames (F j ) from the file system  22 , as indicated by numeral designation  28 . To retrieve the frames, the SRM  26  must first perform a “File Open” function call to the File System  22  to obtain a File Pointer which points to the location of the file containing the header associated with the compressed media data. The SRM  26  then reads the length of the compressed media frame F j  based on this File Pointer and calculates the Frame Pointer pointing to the location of the frame F j  in the file system  22 . The SRM  26  is now ready to fetch the frame data F j  based on the calculated Frame Pointer. Although the SRM  26  described above is shown as a stand alone software module in  FIG. 1 , it is not necessarily to be included as a dedicated software module in the entire system. For example, depending on the implementation, the same functions described above for the SRM  26  can be embedded as an integral part of other software modules. 
     A first Signature Buffer  30  buffers the previously generated signature (S j ). A second Signature Buffer  34  buffers the currently generated unique digital signature (S j+1 ). Thus a signature transition S j+1 →S j  takes place from the second Signature Buffer  34  to the first Signature Buffer  30  when a transition takes place from frame (F j−1 ) to frame (F j ). 
     A third Signature Buffer  38  stores a predefined initial signature (S 0 ). Both of the signature (S 0 ) in the third Buffer  38  and the signature (S j ) in the first Buffer  30  are the two inputs to a 2:1 multiplexer (MUX)  40 . One and only one of these inputs will be selected as the output  41  of the MUX  40  determined by the logic level of the reset signal  18  from the ACM  12 . If the reset signal  18  is set to HIGH (=1), the initial signature (S 0 ) in the third Buffer will be selected as the output  41  of the MUX  40 . If the reset signal  18  is reset to LOW (=0), the previously generated signature (S j ) in the first Buffer  30  will be selected as the output  41  of the MUX  40 . The logic level of the reset signal  18  is normally set to HIGH at the beginning of the entire operation and dropped down to LOW immediately after the very first signature is generated and retained at the LOW level for the rest of the operation so that the previously generated signature (S j ) can always be the output of the MUX  40 . Depending on the implementation, the reset signal  18  can be set to HIGH as many times as desired during the course of the operation. 
     A frame switching means  19  is operatively connected to the SRM  26  and the FSV  15  of ACM  12  for controlling the flow of frames (F j ) from the SRM  26 . If the control signal  39  from FSV  15  is a binary “1”, the frame switching means  19  will be turned “ON” and let the frame (F j ) flow through. If the control signal  39  from FSV  15  is a binary “0”, the frame switching means  19  will be turned “OFF” and the frame (F j ) from the SRM  26  will be discarded and no data will be flown through the frame switching means  19 . 
     A signature switching means  17  is operatively connected to the 2:1 MUX  40  and the SSV  7  of ACM  12  for controlling the flow of signatures (S j ) from the 2:1 MUX  40 . If the control signal  43  from SSV  7  is a binary “1”, the signature switching means  17  will be turned “ON” and let the signature (S j ) flow through. If the control signal  43  from SSV  7  is a binary “0”, the signature switching means  17  will be turned “OFF” and the signature (S j ) from the 2:1 MUX  40  will be discarded and no data will be flown through the signature switching means  17 . 
     A signal generator  42  is operatively connected to the frame switching means  19 , the signature switching means  17 , and to the ACM  12 , for generating a current unique digital signature (S j+1 ) based on: i) the current compressed frame F j , if the frame switching means  19  is “ON”; ii) the output from the 2:1 MUX  40  (either the initial signature S 0  or the previously generated digital signature S j  depending on whether the reset signal  18  is “Set” or “Reset”), if the signature switching means is “ON”; and iii) the status of the enable/disable control signal  16 . If the enable/disable control signal  16  is set to Enable by the ACM  12 , the signature generator  42  will operate normally. However, if the enable/disable control signal  16  is set to Disable by the ACM  12 , the signature generator  42  will be shut down and no signature will be generated, thus no watermark will be created. If both of the frame switching means  19  and the signature switching means  17  are “OFF” while the enable/disable control signal  16  is Enabled, a “null signature” will be generated by the signal generator  42 . The setting of the enable/disable control signal  16  is normally done through a static configuration at the beginning of a recording session. However, a dynamic “re-configuration” of the enable/disable control signal  16  is possible (while a recording session is in progress), providing the new settings are properly kept by the system. The signature generator  42  provides the current signature S j+1    36  to the second signature buffer  34  if the enable/disable control signal  16  is set to Enable. For a production level implementation, any signature generation algorithm, such as the Cyclic Redundancy Code (CRC), can be used in the signature generator  42 . 
     An encryptor  44  receives the unique digital signature (S j+1 )  35  and encrypts the unique digital signature if the enable/disable control signal  16  is set to Enable. Any suitable reversible encryption algorithm (e.g., 64/128-bit AES/DES) can be employed in the encryptor  44 . The encrypted unique digital signature (E j+1 )  24  is stored in the file system  22 . Although (for security reasons) the encryptor  44  is a preferred implementation, it may not constitute a critical element of the present invention. Therefore its implementation may be optionally eliminated. If this is the case, then the unique digital signature (S j+1 )  37  generated by the signature generator  42  will be stored to the file system  22  directly. 
     Referring now to  FIG. 2  and  FIGS. 3A-3I ,  FIG. 2  shows an example during the operation of the present system, designated generally as  55 ; and,  FIGS. 3A-3I  illustrate the  FIG. 2  example with step-by-step details, designated generally as  100 ,  200 ,  300 ,  400 ,  500 ,  500 ,  600 ,  700 ,  800 , and  900 , respectively. As depicted in  FIG. 2 , the length of FCV  71  is 8 (K=8). FCV  71  is loaded with FCV[7:0]=B‘11111001’ and FMV  72  is loaded with FMV[7:0]=B‘10111011’. Both FCV  71  and FMV  72  are ANDed together and the result is stored in FSV  73 , i.e., FSV[7:0]=B ‘10111001’. FSV  73  is outputted serially  74  to the frame switching means  75 . A “1” indicates that the frame switching means  75  will be turned “ON”, whereas a “0” indicates that the frame switching means  75  will be turned “OFF”. The frame switching means  75  controls the flow of the compressed frames  60  from the SRM  66 . A frame will be “selected” as an input to the signature generator  63  if the frame switching means  75  is on. It will be “blocked” (i.e., discarded) if the frame switching means  75  is off. As also depicted in  FIG. 2 , the length of SCV  76  is 6 (L=6). SCV  76  is loaded with SCV[7:0]=B ‘110101’ and SMV  77  is loaded with SMV[7:0]=B‘111111’. Both SCV  76  and SMV  77  are ANDed together and the result is stored in SSV  78 , i.e., SSV[5:0]=B‘110101’. SSV  78  is outputted serially  79  to the signature switching means  80 . A “1” indicates that the signature switching means  80  will be turned “ON”, whereas a “0” indicates that the signature switching means  80  will be turned “OFF”. The signature switching means  80  controls the flow of the signatures  61  outputted from the 2:1 MUX  56 . A signature will be “selected” as an input to the signature generator  63  if the signature switching means  80  is on. It will be “blocked” (i.e., discarded) if the signature switching means  80  is off. An initial signature S 0    62  will be preloaded to the third signature buffer  59  by the application. The generated signatures  64  from the signature generator  63  will be sent to the encryptor, as shown by numeral designation  65 , as well as stored in the second signature buffer  58 . 
     Referring now to  FIG. 3A , in an initial step, designated generally as  100 , before the entire operation starts, the first signature buffer  101 , which is used to store the previously generated signature, will contain some value XX  102  (which is irrelevant to the operation). At the very beginning of the process, both S 0    103  in the third buffer  104  and XX  102  in the first buffer  101  are the inputs to the 2:1 multiplexer  105 . The reset signal  106  is set to HIGH (binary 1) initially by the application. This setting will select the initial signature S 0    107  as the output from the multiplexer  105  and as the input to the signature switching means  108 . Since SSV[0]=B“1”  109 , the signature switching means  108  will be turned on and the signature S 0    107  will be selected and outputted from the signature switching means  108 . The current frame F 0    110 , on the other hand, is inputted to the frame switching means  111 . Since FSV[0]=B‘1’  112 , the frame switching means  111  will be turned on and the frame F 0    110  will be selected and outputted from the frame switching means  111 . Both outputs S 0    107  and F 0    110  will then be concatenated together to form a new frame S 0 ∥F 0    113 , which in turn will be the input to the signature generator  114 . The first signature S 1    115  will then be generated and outputted from the signature generator  114  to the second signature buffer  116  as well as the encryptor  117 . 
     Referring now to  FIG. 3B , in a transition step designated generally as  200 , as soon as the generation of the signature S 1  is completed, as shown in  FIG. 3A , the process transitions from the frame #0 to frame #1. During this transition, the signature S 1   218  residing previously in the second signature buffer  216  will be stored to the first signature buffer  201 . Both of the signatures S 0    203  in the third buffer  204  and S 1    202  in the first buffer  201  are the inputs to the 2:1 multiplexer  205 . The reset signal  206  is set to LOW (binary 0) by the application. This setting will select the signature S 1    207  as the output from the multiplexer  205  and as the input to the signature switching means  208 . Since SSV[1]=B‘0’  209 , the signature switching means  208  will be turned off and the signature S 1    207  will be blocked (discarded) by the signature switching means  208 . The current frame F 1    210 , on the other hand, is inputted to the frame switching means  211 . Since FSV[1]=B‘0’  212 , the frame switching means  211  will be turned off and the frame F 1    210  will be blocked (discarded) by the frame switching means  211 . Since both S 1    207  and F 1    210  are discarded, a “null” frame  213  (i.e., no data) will be the input to the signature generator  214 . The second signature S 2  (null signature)  215  will then be generated and outputted from the signature generator  214  to the second signature buffer  216  as well as the encryptor  217 . 
     Referring now to  FIG. 3C , in a transition step designated generally as  300 , as soon as the generation of the signature S 2  is completed, as shown in  FIG. 3B , the process transitions from the frame #1 to frame #2. During this transition, the signature S 2    318  residing previously in the second signature buffer  316  will be stored to the first signature buffer  301 . Both of the signatures S 0    303  in the third buffer  304  and S 2    302  in the first buffer  301  are the inputs to the 2:1 multiplexer  305 . The reset signal  306  is retained at LOW (binary 0) by the application. This setting will select the signature S 2    307  as the output from the multiplexer  305  and as the input to the signature switching means  308 . Since SSV[2]=B“1”  309 , the signature switching means  308  will be turned on and the signature S 2    307  will be selected and outputted from the signature switching means  308 . The current frame F 2    310 , on the other hand, is inputted to the frame switching means  311 . Since FSV[2]=B‘0’  312 , the frame switching means  311  will be turned off and the frame F 2    310  will be blocked (discarded) by the frame switching means  311 . Since F 2    310  is discarded, only S 2    307  will be the input  313  to the signature generator  314 . The third signature S 3    315  will then be generated and outputted from the signature generator  314  to the second signature buffer  316  as well as the encryptor  317 . 
     Referring now to  FIG. 3D , in a transition step designated generally as  400 , as soon as the generation of the signature S 3  is completed, as shown in  FIG. 3C , the process transitions from the frame #2 to frame #3. During this transition, the signature S 3    418  residing previously in the second signature buffer  416  will be stored to the first signature buffer  401 . Both of the signatures S 0    403  in the third buffer  404  and S 3    402  in the first buffer  401  are the inputs to the 2:1 multiplexer  405 . The reset signal  406  is retained at LOW (binary 0) by the application. This setting will select the signature S 3    407  as the output from the multiplexer  405  and as the input to the signature switching means  408 . Since SSV[3]=B“0”  409 , the signature switching means  408  will be turned off and the signature S 3    407  will be blocked (discarded) by the signature switching means  408 . The current frame F 3    410 , on the other hand, is inputted to the frame switching means  411 . Since FSV[3]=B‘1’  412 , the frame switching means  411  will be turned on and the frame F 3    410  will be selected and outputted from the frame switching means  411 . Since S 3    407  is discarded, only F 3    410  will be the input  413  to the signature generator  414 . The forth signature S 4    415  will then be generated and outputted from the signature generator  414  to the second signature buffer  416  as well as the encryptor  417 . 
     Referring now to  FIG. 3E , in a transition step designated generally as  500 , as soon as the generation of the signature S 4  is completed, as shown in  FIG. 3D , the process transitions from the frame #3 to frame #4. During this transition, the signature S 4    518  residing previously in the second signature buffer  516  will be stored to the first signature buffer  501 . Both of the signatures S 0    503  in the third buffer  504  and S 4    502  in the first buffer  501  are the inputs to the 2:1 multiplexer  505 . The reset signal  506  is set to HIGH (binary 1) by the application. This setting will select the signature S 0    507  as the output from the multiplexer  505  and as the input to the signature switching means  508 . Since SSV[4]=B“1”  509 , the signature switching means  508  will be turned on and the signature S 0    507  will be selected and outputted from the signature switching means  508 . The current frame F 4    510 , on the other hand, is inputted to the frame switching means  511 . Since FSV[4]=B‘1’  512 , the frame switching means  511  will be turned on and the frame F 4    510  will be selected and outputted from the frame switching means  511 . Both outputs S 0    507  and F 4    510  will then be concatenated together to form a new frame S 0 ∥F 4    513 , which in turn will be the input to the signature generator  514 . The fifth signature S 5    515  will then be generated and outputted from the signature generator  514  to the second signature buffer  516  as well as the encryptor  517 . 
     Referring now to  FIG. 3F , in a transition step designated generally as  600 , as soon as the generation of the signature S 5  is completed, as shown in  FIG. 3E , the process transitions from the frame #4 to frame #5. During this transition, the signature S 5    618  residing previously in the second signature buffer  616  will be stored to the first signature buffer  601 . Both of the signatures S 0    603  in the third buffer  604  and S 5    602  in the first buffer  601  are the inputs to the 2:1 multiplexer  605 . The reset signal  606  is reset to LOW (binary 0) by the application. This setting will select the signature S 5    607  as the output from the multiplexer  605  and as the input to the signature switching means  608 . Since SSV[5]=B“1”  609 , the signature switching means  608  will be turned on and the signature S 5    607  will be selected and outputted from the signature switching means  608 . The current frame F 5    610 , on the other hand, is inputted to the frame switching means  611 . Since FSV[5]=B‘1’  612 , the frame switching means  611  will be turned on and the frame F 5    610  will be selected and outputted from the frame switching means  611 . Both outputs S 5    607  and F 5    610  will then be concatenated together to form a new frame S 5 ∥F 5   613 , which in turn will be the input to the signature generator  614 . The sixth signature S 6    615  will then be generated and outputted from the signature generator  614  to the second signature buffer  616  as well as the encryptor  617 . 
     Referring now to  FIG. 3G , in a transition step designated generally as  700 , as soon as the generation of the signature S 6  is completed, as shown in  FIG. 3F , the process transitions from the frame #5 to frame #6. During this transition, the signature S 6    718  residing previously in the second signature buffer  716  will be stored to the first signature buffer  701 . Both of the signatures S 0    703  in the third buffer  704  and S 6    702  in the first buffer  701  are the inputs to the 2:1 multiplexer  705 . The reset signal  706  is retained at LOW (binary 0) by the application. This setting will select the signature S 6    707  as the output from the multiplexer  705  and as the input to the signature switching means  708 . Since SSV[0]=B“1”  709  (note: since the length of SSV is 6, the switch control output from SSV is rapped around and returns back to bit #0, i.e., SSV[0] will be in effect for the current iteration), the signature switching means  708  will be turned on and the signature S 6    707  will be selected and outputted from the signature switching means  708 . The current frame F 6    710 , on the other hand, is inputted to the frame switching means  711 . Since FSV[6]=B‘0’  712 , the frame switching means  711  will be turned off and the frame F 6    710  will be blocked (discarded) by the frame switching means  711 . Since F 6    710  is discarded, only S 6    707  will be the input  713  to the signature generator  714 . The seventh signature S 7    715  will then be generated and outputted from the signature generator  714  to the second signature buffer  716  as well as the encryptor  717 . 
     Referring now to  FIG. 3H , in a transition step designated generally as  800 , as soon as the generation of the signature S 7  is completed, as shown in  FIG. 3G , the process transitions from the frame #6 to frame #7. During this transition, the signature S 7    818  residing previously in the second signature buffer  816  will be stored to the first signature buffer  801 . Both of the signatures S 0    803  in the third buffer  804  and S 7    802  in the first buffer  801  are the inputs to the 2:1 multiplexer  805 . The reset signal  806  is retained at LOW (binary 0) by the application. This setting will select the signature S 7    807  as the output from the multiplexer  805  and as the input to the signature switching means  808 . Since SSV[1]=B“0”  809 , the signature switching means  808  will be turned off and the signature S 7    807  will be blocked (discarded) by the signature switching means  808 . The current frame F 7    810 , on the other hand, is inputted to the frame switching means  811 . Since FSV[7]=B‘1’  812 , the frame switching means  811  will be turned on and the frame F 7    810  will be selected and outputted from the frame switching means  811 . Since S 7    807  is discarded, only F 7    810  will be the input  813  to the signature generator  814 . The eighth signature S 8    815  will then be generated and outputted from the signature generator  814  to the second signature buffer  816  as well as the encryptor  817 . 
     Referring now to  FIG. 3I , in a transition step designated generally as  900 , as soon as the generation of the signature S 8  is completed, as shown in  FIG. 3H , the process transitions from the frame #7 to frame #8. During this transition, the signature S 8    918  residing previously in the second signature buffer  916  will be stored to the first signature buffer  901 . Both of the signatures S 0    903  in the third buffer  904  and S 8    902  in the first buffer  901  are the inputs to the 2:1 multiplexer  905 . The reset signal  906  is retained at LOW (binary 0) by the application. This setting will select the signature S 8    907  as the output from the multiplexer  905  and as the input to the signature switching means  908 . Since SSV[2]=B“1”  909 , the signature switching means  908  will be turned on and the signature S 8    907  will be selected and outputted from the signature switching means  908 . The current frame F 8    910 , on the other hand, is inputted to the frame switching means  911 . Since FSV[0]=B‘1’  912  (note: since the length of FSV is 8, the switch control output from FSV is rapped around and returns back to bit #0, i.e., FSV[0] will be in effect for the current iteration), the frame switching means  911  will be turned on and the frame F 8    910  will be selected and outputted from the frame switching means  911 . Both outputs S 8    907  and F 8    910  will then be concatenated together to form a new frame S 8 ∥F 8   913 , which in turn will be the input to the signature generator  914 . The ninth signature S 9    915  will then be generated and outputted from the signature generator  914  to the second signature buffer  916  as well as the encryptor  917 . 
     Generally speaking, the above process will generate a current unique digital signature S j+1  based on the current compressed frame F j , if the frame switching means is on, and the previously generated digital signature S j , if the signature switching means is on. The current unique digital signature S j+1  thus generated will then be used in conjunction with the next compressed frame F j+1  to generate the next unique digital signature S j+2 . This process continues over and over again till the entire process is terminated or the Enable/Disable signal  16  in system  10  is changed to “Disable” by the application. 
     Although the system of the present invention has been described as having the file system information  20  being provided to the ACM  12  and the ACM  12  providing the reset signal  18  in response to the file system information there are other potential implementations. For example, the reset signal  18  can be set by the ACM  12  per every N frames, where N is an arbitrary positive integer, or set by the ACM  12  whenever a new recording session begins. In general, the reset signal  18  can be set by the ACM  12  in a “random” fashion which is known only to the implementation. Likewise, the values in SCV  1 , SMV  3 , FCV  9 , and FMV  11  in system  10  can all be changed in a “random” fashion which is known only to the implementation. The advantage of controlling the time to set the reset signal  18  and to change the values in SCV  1 , SMV  3 , FCV  9 , and FMV  11  in  10  in a random fashion is that it creates “dynamics” to the signature generation process that is hardly reproduced at the time the media content is ever tampered. 
     As noted above, a fast “False Detection” program can be easily written to detect and identify which frame or frames have been tampered without the need of decoding the entire media content. The writing of such a program can be accomplished by one skilled in the art. For example, if a user&#39;s interest is only to detect if the media content has ever been tampered, a program can be written to re-generate the unique digital signature per each compressed media frame according to the method described in  10 . The identical settings of the reset control signal  18 , SCV  1 , SMV  3 , FCV  9 , FMV  11 , and the enable/disable control signal  16  in  10  which are used to generate the original watermarks will now be used by this program. Since no decompression of the media is needed in this case, the detection program can be implemented very fast. The re-generated signatures will then be compared with the original signatures which are already stored in the file system  22 . If the original signatures were encrypted, they need to be decrypted before the comparison can take place. A “False” is detected if a miss-compare occurs. The False Detection program can also be implemented while the decompression of the media is in progress (i.e., the media is being played back). However in this case, the detection program can only show the detection of the temporal occurrences of tampered frames at the speed of the playback. 
     Other embodiments and configurations may be devised without departing from the spirit of the invention and the scope of the appended claims.