Encoding and detecting apparatus

1. An apparatus for generating a marked copy of an item of material by introducing code words into a copy of the item, the code words being arranged to uniquely identify a data word from a predetermined set of data words each of the data words having at least two fields, the apparatus comprising:

means for generating at least two of the code words having a plurality of code word coefficients, each of the at least two of the code words being independently generated from a different code word seed, one of the at least two of the code words being selected from a first set in a dependence upon a value of a first of the at least two fields and another one of the at least two code words being selected from a second set in a dependence upon a value of a second of the at least two fields, values of the first of the at least two fields being associated with the first set and values of the second of the at least two fields being associated with the second set, the second set being selected in a dependence upon the value of the first of the at least two fields, and

means for combining the plurality of code word coefficients with the item.

2. An apparatus for determining a data word represented by a plurality of code words recovered from a marked material item, the data word including at least two fields, a first of the plurality of code words being associated with a value of a first of the at least two fields and a second of the plurality of code words being associated with a value of a second of the at least two fields in a dependence upon the value of the first of the at least two fields, the apparatus comprising:

means for re-generating selectively each first code word of the plurality of code words associated with a possible value of the first of the at least two fields;

means for arranging for re-generated first code words to be correlated with the recovered code words in a first correlation, each of the first code words being independently generated from a different code word seed;

means for identifying from a result of the first correlation, the value of the first of the at least two fields:

means for re-generating selectively each second code word of the plurality of code words associated with a possible value of the second of the at least two fields, and selected in a dependence upon the value of the first of the at least two fields;

means for arranging for re-generated second code words to be correlated with the recovered code words in a second correlation; and

means for identifying from a result of the second correlation, the value of the second field of the at least two fields.

3. An encoding data processing apparatus for generating a marked copy of an item of material by introducing code words into a copy of the item, the code words being arranged to identify a data word from a set of data words having at least two fields, the apparatus comprising;

a code word generator operable to generate at least two of the code words having a plurality of code word coefficients, each of the at least two of the code words being independently generated from a different code word seed, one of the at least two of the code words being selected from a first set in a dependence upon a value of a first of the at least two fields and another one of the at least two code words being selected from a second set in a dependence upon a value of a second of the at least two fields; and

an encoding processor operable to combine the plurality of code word coefficients with the item, wherein values of the first of the at least two fields are associated with the first set and values of the second of the at least two fields are associated with the second set, the second set being selected in a dependence upon the value of the first of the at least two fields.

4. The encoding data processing apparatus as claimed in claim 3 , wherein the data words are divided into sub-sets, the value of the first of the at least two fields of each of the data words identifying one of the sub-sets, the second set being associated with the values of the second of the at least two fields of the data words within the sub-sets.

5. The encoding data processing apparatus as claimed in claim 4 , wherein the sub-sets contain different numbers of the data words from the set.

6. The encoding data processing apparatus as claimed in claim 4 , wherein a length of the second of the at least two fields is not equal between two of the sub-sets.

7. The encoding data processing apparatus as claimed in claim 3 , wherein,

the values of the first of the at least two fields are uniquely associated with seeds for generating the first set, and

the values of the first of the at least two fields in combination with the values of the second of the at least two fields are uniquely associated wit seeds for generating the second set.

8. The encoding data processing apparatus as claimed in claim 7 , wherein,

the code words are generated from pseudo-random numbers, and

the data words are formed from digits.

9. The encoding data processing apparatus as claimed in claim 3 , wherein each of the at least two fields conveys different types of information.

10. The encoding data processing apparatus as claimed in claim 9 , wherein one of the at least two fields represents a geographical location.

11. The encoding data processing apparatus as claimed in claim 9 , wherein one of the at least two fields represents a time of encoding the item.

12. A cinema projector including the encoding data processing apparatus according to claim 3 , wherein,

the encoding data processing apparatus is operable to receive at least one of audio signals and image signals before a reproduction, and

the encoding data processing apparatus is operable to introduce the code words into the at least one of the audio signals and the image signals before the reproduction.

13. A web server operable to provide material items for downloading via the Internet, the web server including the encoding data processing apparatus according to claim 3 , wherein,

the encoding data processing apparatus is operable to receive the material items, and

the encoding data processing apparatus is operable to introduce a code word into the material items before the material items are downloaded.

14. A method, for an encoding apparatus of generating a marked copy of an item of material by introducing code words into a copy of the item, the code words being arranged to uniquely identify a data word from a predetermined set of data words each of the data words having at least two fields, the method comprising;

generating, with the encoding apparatus, at least two of the code words having a plurality of code word coefficients, each of the at least two of the code words being independently generated from a different code word seed, one of the at least two of the code words being selected from a first set in a dependence upon a value of a first of the at least two fields and another one of the at least two code words being selected from a second set in a dependence upon a value of a second of the at least two fields, values of the first of the at least two fields being associated with the first set and values of the second of the at least two fields being associated with the second set, the second set being selected in a dependence upon the value of the first of the at least two fields, and

combining, with the encoding apparatus, the plurality of code word coefficients with the item.

15. A storage medium providing program code that, when executed by a processor causes the processor to carry out The method according to claim 14 .

16. A method, for a code word detecting apparatus, of determining a data word represented by a plurality of code words recovered from a marked material item, the data word including at least two fields, a first of the plurality of code words being associated with a value of a first of the at least two fields and a second of the plurality of code words being associated with a value of a second of the at least two fields in a dependence upon the value of the first of the at least two fields, the method comprising:

re-generating, with the code word detecting apparatus, selectively each first code word of the plurality of code words associated with a possible value of the first of the at least two fields;

arranging, with the code word detecting apparatus, for re-generated first code words to be correlated with the recovered code words in a first correlation, each of the first code words being independently generated from a different code word seed;

identifying, with the code word detecting apparatus, from a result of the first correlation, the value of the first of the at least two fields;

re-generating, with the code word detecting apparatus, selectively each second code word of the plurality of code words associated with a possible value of the second of the at least two fields and selected in a dependence upon the value of the first of the at least two fields;

arranging, with the code word detecting apparatus, re-generated second code words to be correlated with the recovered code words in a second correlation; and

identifying, with the code word detecting apparatus, from a result of the second correlation, the value of the second of the at least two fields.

17. A detecting data processing apparatus operable to determine at least one data word from code words recovered from a marked material item, the at least one data word including at least two fields, values of a first of the at least two fields being associated with a first set of code words, values of a second of the at least two fields being associated wit a second set of code words, the second set of code words being selected in a dependence upon a value of the first of the at least two fields, the detecting apparatus comprising:

a code word re-generator operable to re-generate code words each having a plurality of code word coefficients and being independently generated from a different code word seed;

a correlator operable to correlate the re-generated code words with the recovered code words; and

a control processor operable to control the code word re-generator to re-generate selectively each first code word associated with a possible value of the first of the at least two fields, to arrange for re-generated first code words to be correlated with the recovered code words in a first correlation, to identify, from a result of the first correlation, the value of the first of the at least two fields, to re-generate selectively each second code word associated with a possible value of the second of the at least two fields and selected in a dependence upon the value of the first of the at least two fields, to arrange for re-generated second code words to be correlated with the recovered code words in a second correlation, and to identify, from a result of the second correlation, a value of the second of the at least two fields.

18. The detecting data processing apparatus as claimed in claim 17 , wherein, for each subsequent field of the at least two fields in the at least one data word, the control processor is operable to re-generate selectively each subsequent code word associated with a possible value of a respective subsequent field, and selected in a dependence upon values of the at least two fields already identified, to arrange for re-generated subsequent code words to be correlated with the recovered code words in a subsequent correlation, and to identify from a result of the subsequent correlation, a value of the respective subsequent field.

19. The detecting data processing apparatus as claimed in claim 17 , wherein each of the code words is generated from a seed, seeds for each possible code word of the code words being stored in a data store, the code word re-generator being arranged to generate the code words in accordance with keys, the plurality of code word coefficients being pseudo-random numbers.

20. The detecting data processing apparatus as claimed in claim 19 , wherein information representing a structure of the at least one data word is stored in the data store for access by the control processor, the structure providing a number of the at least two fields in the at least one data word and a number of digits in each of the at least two fields.

21. The detecting data processing apparatus as claimed in claim 17 , wherein the detecting data processing apparatus is operable to detect more than one of the at least one data word from the code words recovered from the marked material item, the control processor being operable to control the code word re-generator to re-generate selectively each first code word associated with a possible value of the first of the at least two fields of each of the at least one data word, to arrange for the respective re-generated first code word to be correlated wit one of the recovered code words in a respective first correlation, to identify from a result of respective first correlation, a value of the respective first of the at least two fields for each of the at least one data word, to re-generate selectively, for each of the at least one data word, each second code word associated with a possible value of the second of the at least two fields and selected in a dependence upon the respective value of the first of the at least two fields for each of the at least one data word, to arrange for the respective re-generated second code word to be correlated with the one of the recovered code words in a respective second correlation, and to identify from a result of the respective second correlation, a value of the respective second of the at least two fields for each of the at least one data word.