# Patent

## Title
Embedding and decoding three-dimensional watermarks into stereoscopic images

## Abstract

Disclosed inventions relates to methods and systems for encoding at least one watermark into a stereoscopic conjugate pair of images. An example method comprises the step of encoding the at least one watermark by shifting selected pixels of said pair of images in one or more directions. The one or more directions include a horizontal direction. In the disclosed embodiments, ancillary information is not required to support decoding of encoded watermarks in addition to the transmitted left and right images.

## Background
RELATED APPLICATIONS
This application is a continuation of U.S. application Ser. No. 12/581,424, filed on Oct. 19, 2009, now U.S. Pat. No. 8,401,223, which claims the benefit of U.S. Provisional No. 61/106,894, filed Oct. 20, 2008. Each of the above-referenced applications, provisionals and patents is incorporated by reference herein in its entirety.


BACKGROUND OF THE INVENTION
1. Field of the Invention
Embodiments described herein include methods and systems of embedding and decoding three-dimensional watermarks in stereoscopic images.
2. Description of the Related Art
FIG. 1a illustrates a conventional stereoscopic conjugate pair of images. Two images illustrated therein represent the right 101 and left 103 images for a viewer. A viewer wearing a special set of glasses such as the glasses with red-green filters would perceive a 3D image. It should be noted, however, that the red-green filters are included herein only as an example, and other known mechanisms can be employed such as linearly and/or spherically polarized glasses as used within the Real 3D Cinema or Disney Digital 3D systems. Known 3D technologies are described in detail, such as, “3D Standards”, Matt Cowan, Chief Scientific Officer, REAL 3D, Chairman, DC28-40 Stereoscopic Digital Cinema, and “REAL D 3D Theatrical System—A Technical Overview”, Matt Cowan, Chief Scientific Officer, REAL 3D, both of which are incorporated by reference herein in their entirety.
Although only one set of images is represented, many 3D scenes can be collected together and made into a movie. Such a 3D movie that has been digitized will be referred to as three dimensional (3D) video. Example featured movies include “Journey to the Center of the Earth,” and future feature movies include Pixar offerings to include the Toy Story and Cars series. More descriptions of three dimensional movies can be found in “RealD Deal Will Bring 3D To Small Theater Screens”, Sarah McBride, Wall Street Journal, Sep. 2, 2008, “Behind the Scenes of a Next Gen 3D Film,” Cohan Andersen, PC Magazine, Jun. 18, 2008, and “Disney unveils animation slate,” Ben Fritz, Dade Hayes, Variety Magazine, Apr. 8, 2008, all of which are incorporated by reference herein in their entirety.
It should be noted that a 3D effect in 3D images is achieved by shifting pixels in the horizontal direction, along the viewer's eye direction (i.e., x-parallax) to create the illusion of depth in the image scenes. That is, some parts of the 3D image appearing nearer to the viewer while some other parts of the images appearing farther from the viewer. The fused effect creates a perceived 3D depth. This perceived depth is characterized by a depth map 107 shown in FIG. 1b, in which lighter colored portions represent those that appear closer to the viewer compared with darker colored portions. More detailed description of depth map is provided in U.S. Pat. No. 6,215,898, which is incorporated herein its entirety.
FIG. 2 illustrates example watermarks that can be encoded into 3D images. In conventional watermarking methods, watermarks, such as shown in FIG. 2, are encoded into lower bits of color information of 3D images. Although these conventional methods handle 3D object watermarking, these methods' primary focus on the primitive level (e.g. vertices, surfaces) where an object model (e.g. 3D wireframe model) is assumed prior to 3D transmission. The illustrated examples show a watermark 201 created by adjusting three dimensional mesh, and another watermark 203 created by adjusting textures associated with three dimensional model. For such conventional methods, the encoded object's model is necessary in order to decode the watermark.
SUMMARY OF THE INVENTION
Embodiments of the disclosed invention relate to methods, systems, and apparatuses for encoding at least one watermark into a conventional stereoscopic conjugate pair of images. For instance, the method comprises the step of encoding the at least one watermark by shifting selected pixels of said pair of images in one or more directions. The one or more directions include a horizontal direction.
In the disclosed embodiments, ancillary information is not required to support decoding of encoded watermarks in addition to the transmitted left and right images. It should be noted that, herein, the terms embedding watermark(s) is used interchangeable with encoding watermark(s).
In certain embodiments of the present invention, the step of encoding the at least one watermark comprises generating a depth map in a digital format, encoding the at least one watermark into the depth map, thereby generating a encoded depth map, and generating a modified stereoscopic conjugate pair of images based on said encoded depth map and the conventional stereoscopic conjugate pair of images. The step of encoding the at least one watermark may comprise the step of encoding said at least one watermark into one or more least significant bits of said depth map.
Some disclosed embodiments also include the step of encoding at least one of said at least one watermark into each quadrant of at least one stereo image pair. Various embodiments may also include encoding the at least one watermark into a selected image pairs of a 3D movie.
In other example embodiments, a method for decoding at least one watermark from a 3D pair of images that has been encoded with at least one watermark. Embodiments may also include the steps of generating a depth map from the 3D pair of images, receiving information regarding an encoding algorithm that encoded said at least one watermark into said 3D pair of images, and decoding said at least one watermark from said depth map using a decoding algorithm based on said encoding algorithm.
Some example embodiments may also include the steps of modifying said depth map by removing said watermark information from the said depth map, and generating a modified set of 3D pair of images based on the modified depth map. Embodiments can also include the steps of receiving a code from a remote location, matching the code to the at least one watermark, and performing an action based on a result of the matching step.
In some embodiments, the action is preventing the 3D video from being played when the result is a negative match, or the action is reporting to a second remote location when the result is a negative match. The remote location is a database of pass-codes.
Various embodiments of present invention can also be implemented on a processor or processors (e.g., digital signal processors, microprocessors, or the like) coupled to a memory or memories.



BRIEF DESCRIPTION OF THE DRAWINGS
A more complete appreciation of embodiments of the invention, and many of the attendant advantages thereof, will be readily apparent as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawing, wherein:
FIG. 1a is an illustration of a conventional stereoscopic pair of images;
FIG. 1b is an illustration of conventional depth map derived from a stereoscopic pair of images;
FIG. 2 is an illustration of conventional watermarks in 3D scenes;
FIG. 3 is a flow chart illustrating steps of encoding water marks in accordance with various embodiments of the present invention;
FIG. 4 is an illustration of deriving a watermark from a depth map in accordance with various embodiments of the present invention;
FIG. 5 is an illustration of the steps of embedding and then decoding processes using numerical examples in accordance with various embodiments of the present invention;
FIG. 6 is an illustration of example stereoscopic images generated in accordance with various embodiments of the present invention;
FIG. 7 is a flow chart illustrating an example verifying processing chain in accordance with various embodiments of the present invention; and
FIG. 8 is a flow chart illustrating another example verifying processing chain in accordance with various embodiments of the present invention.



It should be noted that a same reference numeral in different figures indicate the same or similar featured functions or items depending on the context.
DESCRIPTION OF VARIOUS EMBODIMENTS OF THE PRESENT INVENTION
To overcome some of the shortcomings described above, in the present invention, ancillary information, for example, is not required to support decoding of encoded watermarks in addition to the transmitted left and right images. It should be noted that, herein, the terms embedding watermark(s) is used interchangeably with encoding watermark(s).
FIG. 3 illustrates example steps of encoding watermarks to 3D images in accordance with various embodiments of the present invention by translating selected pixels in the horizontal and/or vertical directions. In other words, in addition to the pixels being shifted in the original 3D video data to achieve the 3D effect, additional shifting of selected pixels encodes the watermark onto the derived depth map. Because the human eyes are oriented along a horizontal axis, depth is perceived through different perspectives along a horizontal axis. At a minimum, 2 images must be transmitted—one for the left eye and one for the right eye to create a three dimensional scene. Although not inclusive all methodologies to encode the watermark, the following steps provide an example process.
1. Within a video stream, select the target image pair (left 301, right 303).
2. Within an image set, determine the true left and right correspondences between images. These correspondences are generally reported as x shifts between the two images, which is captured as a derived depth map 305.
3. The watermark payload is encoded within these shifts to encode a watermark 307. As an example, the encoded payload can be a serial number, a public key, or a record within a database.
4. Then create updated left and right images 309. In other words, shifts are generated within the left 311 and right 312 images. These images are then transmitted.
It is important to note that the shifts can be generated from the left or right image and the shifts are generally taken in the horizontal direction to be consistent the human eye's frame of reference. This approach is invariant to various image compression techniques and is non-destructive to the original colors in the video signal. The following computer program, written in Java and compiled using Java Development Kit Version 1.4, illustrates the encoding process in more detail.












package vvi.encoders.mpeg2.watermark.*;


/**


 * Filename: DWMEmbedMethod.java


 *


 * This method reads an MPEG-2 file (as an example), encodes a


 * digital watermark, and transmits MPEG-2.


 *


 * For purposes of example, it is assumed that frame[i] is left eye


 * and frame[i+1] is right eye where the display is handled by the


 * stereo application device (e.g. TV, video machine, etc.).


 *


 * Kenneth A. Abeloe - Virginia Venture Industries, LLC


 *


**/


import java.io.IOException;


import java.util.Properties;


import org.apache.log4j.PropertyConfigurator;


public class DWMEmbed {


  public static org.apache.log4j.Logger mLog =


      org.apache.log4j.Logger.getLogger(DWMEmbedMethod.class);


  private DigitalWaterMark dwm;


  // Constructor


  public DWMEmbed(String inputMark, int inFrameRate) {


   // Initialize the Digital Watermark for the Embed Functionality


     dwm = new DigitalWaterMark(inputMark, inFrameRate);


     // Iniitialize the event logger


     initializeLogger( );


  }


  // Initialize the logger


  private void initializeLogger( ) {


   Properties logProperties = new Properties( );


   try {


    logProperties.load(new FileInputStream(“log4j.properties”));


    PropertyConfigurator.configure(logProperties);


    mLog.info(“Logging initialized.”);


   }


   catch(IOException e) {


    throw new RuntimeException(“Unable to load logging property file”,e);


   }


  }


  // Method: Embed Watermark into Video Stream


  public boolean embedWatermark(String inputFileName, String outputFilename) {


    try {


     // Allocate input data streams


     VideoInputStream vin = new VideoInputStream(inputFileName);


     VideoOutputStream vout = new VideoOutputStream(outputFileName);


     // Log values


     mLog.info(“!!! Starting video stream encoding.”);


     // Get properties of video


     VideoProperties vp = new VideoProperties(inputFileName);


     int numLines = vp.getNumLines( );


     int numSamples = vp.getNumSamples( );


     int numColors = vp.getNumColors( );


     // Allocate 2 images - 1 left and 1 right to hold collected video image


      byte[ ][ ] leftImage = new byte[numLines * numSamples][numColors];


      byte[ ][ ] rightImage = new byte[numLines * numSamples][numColors];


      // Pull a left, right image out of the video stream, calculate depth map,


      // embed watermark,


      int index = 0;


      while (vin.play( ) == true) {


       // Grab frames at DWM frame rate specification


       if ((index % dwm.getFrameRate( )) == 0) {


        // Grab frame from image


        // returns numLines * numSamples * numColors


        leftImage = vin.getPixels(index);


        rightImage = vin.getPixels(index+1);


        // Determine depth map


        byte[ ] depthMap = new byte[numLines * numSamples];


        for (int i = 0; i < numLines; i++) {


         for (j = 0; j < numSamples; j++) {


          // Determine depth for current position;


          int pos = i * numSamples + j;


          depth[pos] = findDepth(leftImage[pos],


  rightImage[pos]);


         }


        }


        // Use depth map information to update left / right image


        // with watermark


        leftImage = dwm.updateImage(depth);


        rightImage = dwm.updateImage(depth);


        // Update the video with loaded left and right images.


        vout.createFrame(leftImage, index);


        vout.createFrame(rightImage, index+1);


       } else {


        // Frame is not of interest based on frame rate sampling


        // Update output video with input video only


        vout.createFrame(vin.getPixels(index);


        vout.createFrame(vin.getPixels(index+1);


       }


      } // end of while


      // Write out the video file name


      vout.write( );


      vout.flush( );


     } // end of try


     // Catch any exceptions to the software


     catch(Exception e) {


     mLog.error(“Caught exception in DWMEmbed: ”,e.toString( ));


     return false;


    }


    return true;


  }


  public static void main(String[ ] args) {


     // Digital Watermark Specifics


     int inFrameRate = (int)(new Integer(args[0]).toInt( ));


     // Example String Watermark


     String inDigitalMark = new String(args[1]);


     // Input and Output Filenames


     String inFile = new String(args[2]);


     String outFile = new String(args[3]);


     DWMEbed embedder = new DWMEbed(inFrameRate, inDigitalMark);


     boolean status = embedder(inFile, outFile);


     if (status) {


      mLog.info(“Completed video embedding for the following file: ” + inFile);


      mLog.info(“Completed output video is titled: ” + outFile);


     } else {


      mLog.error(“Errors processing the following input file: ” + inFile);


     }


  }


}









FIG. 4 illustrates the steps of extracting the encoded watermark from the stereoscopic pair with an encoded watermark in accordance with various embodiments of the present invention. In particular, a decoder, which could be part of an apparatus such as a TV, a movie player (e.g., DVDs, high definition DVD such as Blu-Ray Disc players), or a stereoscopic video player, receives the 3D video signal. The signal is first separated into individual image pairs prior to viewing through various methods such as the following:
1. Pixel interleaved—every other pixel belongs to the current view. For example pixel[i] belongs to left view and pixel[i+1] belongs to right view.
2. Line interleaved—every other line belongs to the current view. For example pixel[i] through pixel[i+numSamples] belongs to the left view while pixel[i+numSamples+1] belongs to the right view.
3. Scene interleaved—every other image belongs to the current view.
It should be noted that all image pairs could be encoded with watermarks or only selected image pairs can be encoded with watermarks. In reference to FIG. 4, for the image pairs (e.g., left image 401 and right image 403) with encoded watermarks, the depth map 405 is derived. From the derived depth map, the encoded watermark 407 is extracted. The following computer program, written in Java and compiled using the Java Development Kit Version 1.4, illustrates the encoding process in more detail.












package vvi.encoders.mpeg2.watermark.*;


/**


 * Filename: DWMDecodeMethod.java


 *


 * This method reads an MPEG-2 file (as an example), decodes the


 * digital watermark and updates a log file with results.


 *


 * For purposes of example, it is assumed that frame[i] is left eye


 * and frame[i+1] is right eye where the display is handled by the


 * stereo application device (e.g. TV, video machine, etc.).


 *


 * Kenneth A. Abeloe - Virginia Venture Industries, LLC


 *


**/


import java.io.IOException;


import java.util.Properties;


import org.apache.log4j.PropertyConfigurator;


public class DWMDecode {


  public static org.apache.log4j.Logger mLog =


       org.apache.log4j.Logger.getLogger(DWMEmbedMethod.class);


  private DigitalWaterMark dwm;


  // Constructor


  public DWMDecode(int inFrameRate) {


     // Initialize the Digital Watermark for the Decode Functionality


     dwm = new Digital WaterMark(null, inFrameRate);


     // Iniitialize the event logger


     initializeLogger( );


  }


  // Initialize the logger


  private void initializeLogger( ) {


   Properties logProperties = new Properties( );


   try {


    logProperties.load(new FileInputStream(“log4j.properties”));


    PropertyConfigurator.configure(logProperties);


    mLog.info(“Logging initialized.”);


   }


   catch(IOException e) {


    throw new RuntimeException(“Unable to load logging property file”,e);


   }


  }


  // Method: Decode Watermark from Video Stream


  public boolean decodeWatermark(String inputFileName) {


    try {


      // Allocate input data streams


      VideoInputStream vin = new VideoInputStream(inputFileName);


      // Log values


      mLog.info(“!!! Starting video stream decoding.”);


      // Get properties of video


      VideoProperties vp = new VideoProperties(inputFileName);


      int numLines = vp.getNumLines( );


      int numSamples = vp.getNumSamples( );


      int numColors = vp.getNumColors( );


      // Allocate 2 images - 1 left and 1 right to hold collected video image


      byte[ ][ ] leftImage = new byte[numLines * numSamples][numColors];


      byte[ ][ ] rightImage = new byte[numLines * numSamples][numColors];


      // Pull a left, right image out of the video stream, calculate depth map,


      // embed watermark,


      int index = 0;


      while (vin.play( ) == true) {


       // Grab frames at DWM frame rate specification


       if ((index % dwm.getFrameRate( )) == 0) {


        // Grab frame from image


        // returns numLines * numSamples * numColors


        leftImage = vin.getPixels(index);


        rightImage = vin.getPixels(index+1);


        // Determine depth map


        byte[ ] depthMap = new byte[numLines * numSamples];


        for (int i = 0; i < numLines; i++) {


         for (j = 0; j < numSamples; j++) {


          // Determine depth for current position;


          int pos = i * numSamples +j;


          depth[pos] = findDepth(leftImage[pos],


rightImage[pos]);


         }


        }


        // Use depth map information to determine digital mark


        if (dwm.decodeMark(depth)) {


         mLog.info(“Watermark Determined to be: ” + dwm.toString( ));


        } else {


         mLog.error(“Error determining watermark for index: ” +


index);


        } }


      } // end of while


     } // end of try


     // Catch any exceptions to the software


     catch(Exception e) {


     mLog.error(“Caught exception in DWMEmbed: ”,e.toString( ));


     return false;


    }


    return true;


  }


  public static void main(String[ ] args) {


     // Digital Watermark Specifics


     int inFrameRate = (int)(new Integer(args[0]).toInt( ));


     DWMDecode decoder = new DWMDecode(inFrameRate);


     boolean status = decoder(inFile);


     if (status) {


       mLog.info(“Completed video decoding for the following file: ” + inFile);


     } else {


       mLog.error(“Errors processing the following input file: ” + inFile);


     }


  }


 }









Various embodiments of the present invention can include both encoding and decoding function. The following explains an example process for adding watermark information into the depth map for a particular set of images (left, right) within a 3D video. In this example, the digital watermark to be encoded is a string to be encoded multiple times in the 3D scene.
1. The string is encoded into a binary format. FIG. 5 illustrates an example binary string to encode 501. As another example, a part of the string “elephant” can be encoded in the binary representation of the following: 0110010101101100011001010111000001101000011000010110111001110100
2. The depth map from a pair of stereo images (not yet embedded with a watermark) is derived by correlating features along the horizontal direction (or x direction) between left and right. For example purposes only, for every pixel in the left image, search along the x-direction for pixel correspondence (e.g. through correlation) in the right image. FIG. 5 show a part of an example depth map 503.
The following computer program, written in Java and compiled using Java Development Kit Version 1.4, illustrates the encoding process in more detail.












short[ ] depthMap = new short[TotalLines][TotalSamples];


// Loop through all lines and samples of the image


for (int i = 0; i < TotalLines; i++) {


 for (int j = 0; j < TotalSamples; j++) {


  Initialize the local variables.


  double matchResult;


  double maxResult = 0.0;


  // Chip the left image (reference image)


  tstLeftImage = chipImage(i, j, 20, 20, leftImage);


  // Search a window of values in the X direction


  for (k = j−20; k <= j+20; k++) {


   try {


    // Chip various right images (test images)


    tstRightImage = chipImage(i, k, 20, 20, rightImage);


    // Correlate the images together


    matchResult = correlateImages(tstLeftImage, tstRightImage);


    // Use maxResult to indntify the best match


    if (matchResult > maxResult) {


     maxResult = matchResult;


     resultIndex = k;


    }


   }


   // Catch any reading exceptions (e.g. borders) and keep going.


   catch (Exception e) {


    continue;


   }


  }


  // Delta difference between left and right image


  depthMap[i][j] = k − j;


 }


}









3. As an example, the string is encoded by examining and regenerating the depth map using the binary encoded string. As shown by a string 505 in FIG. 5, a binary string representing one line of a watermark can be encoded using an odd/even scheme within the depth map. Even numbers in the depth map register to a binary value “0” and odd numbers in the depth map register to a binary value “1”. As shown by a string 507 in FIG. 5, the depth map is adjusted to support the encoded string. This process is repeated multiple times to help defeat tampering attempts on the processed video.
4. After the depth map has been adjusted to encode the value of the watermark, the depth values are translated back to the original image in the forms of depth shifts in the image as shown in FIG. 6, in which 601 is a representative stereo image pair without a digital watermark, 603 is a representative stereo image pair with a digital watermark. In this example, in 603, an example “elephant” string has been embedded.
In this example, the digital watermark to be extracted is a string to be decoded from the 3D scene.
1. The depth map is derived by correlating features along the horizontal direction (or x direction) between left and right. For example purposes only, for every pixel in the left image, search along the x-direction for pixel correspondence (e.g. through correlation) in the right image (as shown above).
2. The depth values are analyzed for their odd/even values and either translated into a binary 0 for even numbers or a binary 1 for odd numbers (see string 505 in FIG. 5). Because multiple digital watermarks may have been introduced into the depth map, special characters (e.g., 00000000) may be introduced to break up the multiple watermarks.
3. Once the binary string is determined, the string is converted into ASCII and transmitted for verification processes.
FIGS. 7 and 8 illustrate the example uses of the decoded (or extracted) watermark information. In FIG. 7, in a retrieve watermark step 703, the watermark information transmitted along with the 3D video signal (e.g., the closed caption data 705) is retrieved. The retrieved watermark information is compared with the watermark information decoded from the derived depth map 707 in a verify step 709. If the decoded watermark information matches with the watermark information retrieved in step 703, the 3D video is played on a video play system 711 stereoscopically using, for example, red and green filters. If the decoded watermark information does not match with the watermark information retrieved in step 703, the 3D video is not played. In FIG. 8, the decoded watermark information is compared with the watermark information stored in an external source, such as a database, retrieved by a data server 801 in a retrieve watermark step 803. The retrieved watermark in these examples can also be used to verify the video content, provide ancillary information to the viewer (e.g., promotions, games, extras). The system could verify content by checking an encoded specific product identifier (e.g., serial number) versus the database specific product identifier.
While the invention has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiments for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.

## Claims

1. A method for encoding at least one watermark using a 3D pair of images by shifting one or more pixels in one or more directions, the method comprising:
generating a depth map from the 3D pair of images;
modifying said depth map to encode the at least one watermark into said depth map; and
generating a modified 3D pair of images based on the modified depth map.

2. The method of claim 1, further comprising:
receiving information of an encoding algorithm for modifying said depth map to encode said at least one watermark into said depth map; and
using the encoding algorithm to encode the at least one watermark into said depth map.

3. The method of claim 1, further comprising:
determining a code associated with the at least one watermark;
providing the code to an external device;
matching the code to the at least one watermark in the external device; and
performing an action based on whether the code matches the watermark.

4. The method of claim 3, wherein the action comprises preventing a three dimensional video, that includes the 3D pair of images, from being played when the code does not match the at least one watermark.

5. A system of encoding at least one watermark into a stereoscopic conjugate pair of images, the system comprising:
a generator configured to create a depth map from the stereoscopic conjugate pair of images; and
an encoder configured to encode said at least one watermark into the depth map creating a modified depth map.

6. The system of claim 5, further comprising a processor configured to create an updated stereoscopic conjugate pair of images from the modified depth, the updated stereoscopic conjugate pair of images having one or more selected pixels shifted in one or more directions when compared to the original stereoscopic conjugate pair of images, wherein the one or more directions includes a horizontal direction.

7. The system of claim 5, wherein said having one or more selected pixels shifted in one or more directions includes shifting one or more least significant bits of said selected pixels positions to encode said at least one watermark.

8. The system of claim 5, wherein said shifted selected pixels includes pixels selected in each quadrant of at least one of the conjugate pair of images to thereby encode said at least one watermark.

9. The system of claim 5, wherein said stereoscopic conjugate pair of images pair is a part of a three dimensional movie.

10. A non-transitory computer readable medium comprising instructions that, when executed, cause an apparatus to perform a method for decoding at least one watermark from a stereoscopic conjugate pair of images, the method comprising:
generating a depth map from the 3D pair of images;
decoding said at least one watermark from said depth map;
modifying said depth map by removing said watermark information from the said depth map, and
generating a modified set of three dimensional pair of images based on the modified depth map.

11. The computer readable medium of claim 10, wherein the method further comprises:
receiving information regarding an encoding algorithm that encoded said at least one watermark into said 3D pair of images, and
using a decoding algorithm based on said encoding algorithm.

12. The computer readable medium of claim 10, wherein the method further comprises:
receiving a code from an external source;
matching the code to the at least one watermark; and
performing an action based on a result of said matching.