Tamper detection of documents using encoded dots

A method of ensuring that unauthorised changes to an unprotected document can be detected, the method comprising an encoding process and a decoding process;

• wherein:
• the encoding process comprises the steps of:
• defining an unmodulated array of protection marks, and for each protection mark in the array:
• modulating an attribute of the protection mark according to a property of the unprotected document in an area associated with the protection mark;
• wherein the area associated with the protection mark overlaps an area associated with another protection mark in the array;
• and
• incorporating the modulated protection marks into the unprotected document to thereby form a protected document;
• and wherein:
• the decoding process comprises the steps of:
• extracting a description of the unmodulated array of protection marks from the protected document;
• identifying the modulated protection marks in the protected document;
• and for each identified modulated protection mark;
• demodulating the attribute of the modulated protection mark;
• determining from the demodulated attribute the corresponding property of the unprotected document;
• determining the property of the protected document in the area associated with the modulated protection mark;
• and
• comparing the determined corresponding property of the unprotected document to the determined property of the protected document.

A method of detecting unauthorised changes to a protected document, the method comprises the steps of:

• extracting a description of an unmodulated array of protection marks from the protected document;
• identifying modulated protection marks in the protected document;
• and for each identified modulated protection mark;
• demodulating an attribute of the modulated protection mark;
• determining from the demodulated attribute a corresponding property of a corresponding unprotected document;
• determining the property of the protected document in an area associated with the modulated protection mark;
• comparing the determined corresponding property of the unprotected document to the determined property of the protected document;
• and
• determining if unauthorised changes have been made to the protected document dependent upon the comparing step.

A system for ensuring that unauthorised changes to an unprotected document can be detected, the system comprising an encoding sub-system and a decoding sub-system, wherein:

• said encoding sub-system comprises:
• a memory for storing a program;
• and
• a processor for executing the program, said program comprising:
• code for defining an unmodulated array of protection marks, and for each protection mark in the array:
• code for modulating an attribute of the protection mark according to a property of the unprotected document in an area associated with the protection mark;
• wherein the area associated with the protection mark overlaps an area associated with another protection mark in the array;
• and
• code for incorporating the modulated protection marks into the unprotected document to thereby form a protected document;
• and wherein:
• the decoding sub-system comprises:
• a memory for storing a program;
• and
• a processor for executing the program, said program comprising:
• code for extracting a description of the unmodulated array of protection marks from the protected document;
• code for identifying the modulated protection marks in the protected document;
• and for each identified modulated protection mark;
• code for demodulating the attribute of the modulated protection mark;
• code for determining from the demodulated attribute the corresponding property of the unprotected document;
• code for determining the property of the protected document in the area associated with the modulated protection mark;
• and
• code for comparing the determined corresponding property of the unprotected document to the determined property of the protected document.

A encoding sub-system for a system for ensuring that unauthorised changes to an unprotected document can be detected, the system comprising an encoding sub-system and a decoding sub-system, wherein said encoding sub-system comprises:

• a memory for storing a program;
• and
• a processor for executing the program, said program comprising:
• code for defining an unmodulated array of protection marks, and for each protection mark in the array:
• code for modulating an attribute of the protection mark according to a property of the unprotected document in an area associated with the protection mark;
• wherein the area associated with the protection mark overlaps an area associated with another protection mark in the array;
• and
• code for incorporating the modulated protection marks into the unprotected document to thereby form a protected document.

A decoding sub-system for detecting unauthorised changes to a protected document, the sub-system comprising:

• a memory for storing a program;
• and
• a processor for executing the program, said program comprising:
• code for extracting a description of an unmodulated array of protection marks from the protected document;
• code for identifying modulated protection marks in the protected document;
• and for each identified modulated protection mark;
• code for demodulating an attribute of the modulated protection mark;
• code for determining from the demodulated attribute a corresponding property of a corresponding unprotected document;
• code for determining the property of the protected document in an area associated with the modulated protection mark;
• code for comparing the determined corresponding property of the unprotected document to the determined property of the protected document;
• and
• code for determining if unauthorised changes have been made to the protected document dependent upon the comparing step.

A computer program product including a computer readable medium having recorded thereon a computer program for directing a processor to execute a method for ensuring that unauthorised changes to an unprotected document can be detected, the program comprising, in relation to an encoding sub-system:

• code for defining an unmodulated array of protection marks, and for each protection mark in the array:
• code for modulating an attribute of the protection mark according to a property of the unprotected document in an area associated with the protection mark;
• wherein the area associated with the protection mark overlaps an area associated with another protection mark in the array;
• and
• code for incorporating the modulated protection marks into the unprotected document to thereby form a protected document;
• and wherein the program comprises in relation to a decoding sub-system:
• code for extracting a description of the unmodulated array of protection marks from the protected document;
• code for identifying the modulated protection marks in the protected document;
• and
• for each identified modulated protection mark;
• code for demodulating the attribute of the modulated protection mark;
• code for determining from the demodulated attribute the corresponding property of the unprotected document;
• code for determining the property of the protected document in the area associated with the modulated protection mark;
• and
• code for comparing the determined corresponding property of the unprotected document to the determined property of the protected document.

A computer program product including a computer readable medium having recorded thereon a computer program for directing a processor to execute an encoding method for ensuring that unauthorised changes to an unprotected document can be detected, the program comprising:

• code for defining an unmodulated array of protection marks, and for each protection mark in the array:
• code for modulating an attribute of the protection mark according to a property of the unprotected document in an area associated with the protection mark;
• wherein the area associated with the protection mark overlaps an area associated with another protection mark in the array;
• and
• code for incorporating the modulated protection marks into the unprotected document to thereby form a protected document.

A computer program product including a computer readable medium having recorded thereon a computer program for directing a processor to execute a decoding method for ensuring that unauthorised changes to an unprotected document can be detected, the program comprising:

• code for extracting a description of an unmodulated array of protection marks from the protected document;
• code for identifying modulated protection marks in the protected document;
• and for each identified modulated protection mark;
• code for demodulating an attribute of the modulated protection mark;
• code for determining from the demodulated attribute a corresponding property of a corresponding unprotected document;
• code for determining the property of the protected document in an area associated with the modulated protection mark;
• code for comparing the determined corresponding property of the unprotected document to the determined property of the protected document;
• and
• code for determining if unauthorised changes have been made to the protected document dependent upon the comparing step.

A method of generating a protected document containing content and data, said data being encoded in a plurality of marks, the method comprising the steps of:

• identifying a location on the grid for encoding data;
• associating an area of the document with the location, the area comprising at least a portion of the content;
• determining a parameter based on a property of the content of the area of the document;
• and
• encoding said determined parameter at the location using a modulated mark to thereby form a protected document.