System for detecting photocopied or laser-printed documents

• US 20020037093A1
• Filed: 03/05/2001
• Published: 03/28/2002
• Est. Priority Date: 06/10/1998
• Status: Active Grant

• Current Assignee: Stephen C. Murphy
• Original Assignee: Stephen C. Murphy
• Inventors: Murphy, Stephen C.
• Granted Patent: US 6,571,001 B2
• Time in Patent Office: Days
• US Class Current: 382/112
• CPC Class Codes: G06V 30/2455 Discrimination between machine-print, hand-print and cursive writing
• CPC Class Codes: H04N 1/00002 Diagnosis, testing or measuring; Detecting, analysing or monitoring not otherwise provided for error detection, error correction or monitoring in digital computers or digital computer components G06F11/00
• CPC Class Codes: H04N 1/00005 relating to image data
• CPC Class Codes: H04N 1/00037 Detecting, i.e. determining the occurrence of a predetermined state H04N1/00031 takes precedence
• CPC Class Codes: H04N 1/00039 Analysis, i.e. separating and studying components of a greater whole
• CPC Class Codes: H04N 1/00047 using an image not specifically designed for the purpose
• CPC Class Codes: H04N 1/00068 Calculating or estimating
• CPC Class Codes: H04N 1/00074 Indicating or reporting details of user-machine interface H04N1/0035
• CPC Class Codes: H04N 1/00092 relating to the original or to the reproducing medium, e.g. imperfections or dirt detecting properties of a sheet H04N1/00681

Abstract

A system for distinguishing photocopied or laser-printed documents from original documents produced by offset printing, handwriting, or typewriting. The system scans a document at low-resolution and at high-resolution to produce a low-resolution and a high-resolution matrix representation of the presence or absence of ink or toner at discrete locations on the surface of the document. Printed regions detected by the system at low-resolution are used to mask regions of the high-resolution matrix representation from the analysis. The remaining unmasked regions of the high-resolution matrix representation are analyzed by the system to detect discrete microdots uniformly distributed within those regions. The presence of microdots on the surface of the document indicates that the document was produced as a photocopied or a laser-printed duplicate.

Claims

1. A system for determining whether a document has been created by photocopying or laser printing, the system comprising:

a detector that detects microdots of toner or other substances employed in photocopying and laser printing on the surface of a document; and

an output device that, in response to detection by the detector of microdots of toner or other substances employed in photocopying and laser printing on the surface of a document, outputs an indication that the document has been created by photocopying or laser printing.

2. The system of claim 1 wherein the detector further comprises:

an optical scanner that measures the reflectivity of a portion of the surface of the document, the result of measurement of the reflectivity of the surface of the document output as a scan; and

a computing device that identifies and counts indications of microdots within the scan, that compares the count of microdots to a threshold value, and that outputs to the output device an indication that the document has been created by photocopying or laser printing when the count of microdots exceeds the threshold value.

3. The system of claim 2 wherein:

the optical scanner measures the reflectivity of the portion of the surface of the document at low resolution to produce a low-resolution scan in which microdots are not detectable; and

the optical scanner measures the reflectivity of the surface of the area of the document at high resolution to produce a high-resolution scan in which microdots are detectable.

4. The system of claim 3 wherein the computing device identifies and counts microdots in that portion of the high-resolution scan that corresponds to those portions of the low-resolution scan in which the measured reflectivity does not indicate the presence of ink, toner, and other printing substances.

5. The system of claim 4 wherein the computing device identifies microdots as small regions within the high-resolution scan that differ in reflectivity from the reflectivity of unprinted regions of the document.

6. The system of claim 5 wherein the high-resolution scan comprises a high-resolution matrix having cells that each contain a value that indicates the reflectivity at a corresponding position on the surface of the document, the area of the surface of the document corresponding to each cell of the high-resolution matrix approximately equal to the area of a microdot.

7. The system of claim 6 wherein the computing device identifies as an indication of a microdot a high-resolution matrix cell having a value indicating a reflectivity corresponding to ink, toner, or other printing substances adjoining on all sides high-resolution matrix cells having values indicating a reflectivity corresponding to an unprinted surface of the document.

8. The system of claim 6 wherein the computing device identifies as as an indication of a microdot two high-resolution matrix cells, adjoined along a common side, having values indicating a reflectivity corresponding to ink, toner, or other printing substances and adjoining on all sides other than the common side high-resolution matrix cells having a value indicating a reflectivity corresponding to an unprinted surface of the document.

9. A system for determining whether a document on which one or more images have been created has been printed by photocopying or laser printing, the system comprising:

a scanning device that scans a portion the document at low resolution to produce a low-resolution scan and that scans the blank areas of the document at high resolution to produce a high-resolution scan; and

a computing device that analyzes the low-resolution scan to identify blank areas of the document on which the one or more of the images have not been created and that analyzes the high-resolution scan to detect microdots of toner or other substances employed in photocopying and laser printing.

10. The system of claim 9 wherein the low-resolution scan comprises a low-resolution matrix having cells, each cell containing a value that indicates presence or absence of toner or other substances employed in photocopying and laser printing at a position on the document corresponding to the cell and wherein the high-resolution scan comprises a high-resolution matrix having cells, each cell containing a value that indicates presence or absence of toner or other substances employed in photocopying and laser printing at a position on the document corresponding to the cell.

11. The system of claim 10 wherein an area of the document corresponding to one high-resolution matrix cell is approximately equal to the area of a microdot.

12. The system of claim 11 wherein the computing device identifies microdots of toner or other substances employed in photocopying and laser printing by identifying high-resolution matrix cells that have a value that indicates presence of toner or other substances employed in photocopying and laser printing and that share common sides with adjoining high-resolution matrix cells that all have values that indicate absence of toner or other substances employed in photocopying and laser printing.

13. The system of claim 12 wherein the computing device identifies microdots of toner or other substances employed in photocopying and laser printing by identifying pairs of high-resolution cells that share a common side, that have values that indicate presence of toner or other substances employed in photocopying and laser printing, and that adjoin on all sides other than the common shared side high-resolution cells that all have values that indicate absence of toner or other substances employed in photocopying and laser printing.

15. The system of claim 14 wherein the computed value is the number of microdots within the analyzed area divided by the size of the analyzed area and the threshold value is a threshold density of microdots.

16. The system of claim 14 wherein the scanning device is an optical scanner that measures the reflectivity of the surface of the document.

17. The system of claim 14 wherein the scanning device scans the area of the document for the presence of substances at a lower resolution at which microdots are not detectable and the computing device analyzes that portion of the area at high resolution that corresponds to those areas of the low resolution scan on which the presence of a substance was not detected.

18. The system of claim 17 wherein the scanning device, after scanning the area of the document for the presence of substances at low resolution, produces a low-resolution matrix having cells that each contain a value that indicates that the presence or absence of a substance at corresponding position on the surface of the document and wherein the scanning device, after scanning the area of the document for the presence of substances at high resolution, produces a high-resolution matrix having cells that each contain a value that indicates that the presence or absence of a substance at corresponding position on the surface of the document.

19. The system of claim 18 wherein the resolution of the high-resolution scan is chosen so that a dimension of the area of the surface of the document corresponding to a cell of the high-resolution matrix is approximately equal to the average diameter of a microdot and wherein analyzing that portion of the area at high resolution that corresponds to those areas of the low resolution scan on which the presence of a substance was not detected further includes:

initializing a count of detected microdots to 0;

successively choosing each unanalyzed cell within a portion of cells of the high-resolution matrix for analysis; and

when the value of the chosen cell indicates presence of a substance and the value of the cell of the low-resolution matrix that corresponds to the chosen cell indicates absence of a substance and the chosen cell has at most one adjacent high-resolution cell with a value indicating presence of a substance and has no additional adjacent high-resolution cells with a value indicating presence of a substance, determining that the chosen cell and the at most one adjacent cell comprise an indication of a microdot and incrementing the count of detected microdots by one.

14. A system for determining whether a document was produced by photocopying or laser-printing, the system comprising:

a scanning device that scans an area of the document for the presence of substances, such as ink and toner, that differ in reflectivity from a background reflectivity of the document at a resolution sufficient to detect microdots characteristic of photocopied or laser-printed documents;

a computing device that analyzes an area of the scanned area to count the number of microdots within the analyzed area, that computes a value based on the number of microdots counted, and that compares the computed value to a threshold value; and

an output to which the computing device outputs an indication that the document was produced by photocopying or laser-printing when the computed value exceeds the threshold value and to which the computing device outputs an indication that the document was not produced by photocopying or laser-printing when the computed value is equal to or less than the threshold value.

20. A system for detecting small discreet microdots of ink, toner, and other substances employed in photocopying and laser printing on the surface of a document, the system comprising:

a scanning device that scans a portion the document at low resolution to produce a low-resolution matrix, each cell of the low-resolution matrix corresponding to a discrete low-resolution region on the surface of the document and having a value that indicates whether a photocopying or laser printing substance was detected on that region of the document, the discrete low-resolution region on the surface sufficiently large, and the threshold for substance detection sufficiently high, that a presence of a number of microdots within a discrete low-resolution region otherwise free of photocopying or laser printing substances is not detected, the scanning device also scanning the portion the document at high resolution to produce a high-resolution matrix, each cell of the high-resolution matrix corresponding to a discrete high-resolution region on the surface of the document smaller than a discrete low-resolution region corresponding to a low-resolution matrix cell and having a value that indicates whether a photocopying or laser printing substance was detected on the high-resolution region of the document, a high-resolution region sufficiently small, and the threshold for substance detection sufficiently low, that a presence of a number of microdots within a discrete high-resolution region otherwise free of photocopying or laser printing substances is detected; and

a computing device that compares the low-resolution matrix to the high-resolution matrix in order to detect indications of microdots.

21. The system of claim 20 wherein a dimension of the high-resolution region is approximately equal to the average diameter of a microdot.

22. The system of claim 21 wherein the low-resolution and high-resolution matrices are aligned by the computing device so that the upper left-hand portion of the portion of the document corresponding to the first cell of the low-resolution matrix corresponds to first element of the high-resolution matrix and so that the portion of the document represented by the low-resolution matrix is equal to the portion of the document represented by the high-resolution matrix, each cell of the low-resolution matrix corresponding to a number of cells of the high-resolution matrix.

23. The system of claim 22 wherein the computing device compares the low-resolution matrix to the high-resolution matrix by:

choosing as a candidate cell each successive, unanalyzed cell of a contiguous set of cells within the high-resolution matrix that has a value indicating detection of a photocopying or laser printing substance and that corresponds to a low-resolution matrix cell that has a value indicating that a photocopying or laser printing substance was not detected; and

for each candidate cell,

when the candidate cell has one adjoining, unanalyzed cell that has a value indicating detection of a photocopying or laser printing substance and that corresponds to a low-resolution matrix cell that has a value indicating that a photocopying or laser printing substance was not detected and when the adjoining cell has no adjoining cells in addition to the candidate cell that have a value indicating detection of a photocopying or laser printing substance, analyzing the candidate cell and the one adjoining cell together as a candidate microdot; and

when the candidate cell has no adjoining cells that have a value indicating detection of a photocopying or laser printing substance, analyzing the candidate cell as a candidate microdot.

24. The system of claim 23 wherein analysis of a candidate microdot by the computing device comprises:

determining whether any cell adjoining the candidate microdot correspond to a low-resolution matrix cell that has a value indicating detection of a photocopying or laser printing substance;

when no cell adjoining the candidate microdot corresponds to a low-resolution matrix cell that has a value indicating detection of a photocopying or laser printing substance, determining that the candidate microdot is an indication of a microdot; and

when a cell adjoining the candidate microdot corresponds to a low-resolution matrix cell that has a value indicating detection of a photocopying or laser printing substance, determining that the candidate microdot is not an indication of a microdot.

25. The system of claim 20 wherein the scanning device is an optical scanner that measures the reflectivity of the surface of the document.