Method for detecting forged barcodes
View Patent ↗A method of printing a two-dimensional barcode by tilting the print head, which results in tilted barcode, and methods of detecting various types of attempts to forge the tilted barcode including: (i) a low level forgery that consists of a simple scan and reprint of the barcode, (ii) a low level forgery that consists of a reproduction (i.e., a read and regeneration) and subsequent printing of the barcode using a printer with a non-tilted print head by a fraudster that is not aware of the tilt in the original barcode, and (iii) a higher level forgery by a fraudster that is aware of the tilt in the original barcode and that digitally tilts/shears an image of the barcode and prints the digitally tilted/sheared image using a printer with a non-tilted print head in an effort to mimic the tilt present in the legitimate barcode.
1. A method of determining whether a printed barcode is a forgery of a legitimate barcode, wherein said legitimate barcode is printed by a print head by moving a print medium relative to said print head along a first axis, the method comprising:
obtaining an electronic image of said printed barcode wherein by scanning said printed bar code with a scanner having a scanning grid columns of printed pixels produced by said print head are tilted from a second axis perpendicular to said first axis by an angle α, and wherein said legitimate barcode has a first edge portion that is parallel to said first axis and a second edge portion that is tilted with respect to said second axis by said angle α and said second scanned edge portion at least partially covers a first column of pixels and a second column of pixels of said scanning grid,
determining from said image a first scanned edge portion and a second scanned edge portion;
determining an angle R 2 of the first scanned edge portion relative to a first scanner axis;
determining an angle R 1 of the second scanned edge portion relative to a second scanner axis perpendicular to the first scanner axis; by generating a first greyness curve for said first column and a second greyness curve for said second column;
measuring a distance D, said distance D being equal to the number of pixels between a first pixel in said first column having a pre-selected greyness value from said first greyness curve and a second pixel in said second column having said pre-selected greyness value from said second greyness curve; and
calculating said angle R 1 according to the following formula: π/2−arctan(D/d), wherein d is the number of pixels separating said first column and said second column,
determining a tilt angle R 1 -R 2 ; and
determining that said printed barcode is a forgery if said tilt angle is not substantially equal to said angle α.
2. The method according to claim 1 , wherein said step of determining that said printed barcode is a forgery if said tilt angle is not substantially equal to said angle α comprises determining that said printed barcode is a forgery if said tilt angle is more than a predetermined amount different than said angle α.
3. The method according to claim 1 , further comprising determining a first variance in a plurality of first grey levels obtained from said second scanned edge portion, and determining that said printed barcode is a forgery if said first variance is greater than a predetermined threshold value.
4. The method according to claim 3 , further comprising determining a second variance in a plurality of second grey levels obtained from said first scanned edge portion, and determining that said printed barcode is a forgery if one or both of said first variance and said second variance is greater than said predetermined threshold value.
5. The method according to claim 3 , further comprising determining a second variance in a plurality of second grey levels obtained from said first scanned edge portion, and determining that said printed barcode is a forgery if an average of said first variance and said second variance is greater than said predetermined threshold value.
6. The method according to claim 1 , wherein said first scanned edge portion at least partially covers a first row of pixels and a second row of pixels of said scanning grid, and wherein said method further comprises determining said angle R 2 by:
generating a third greyness curve for said first row and a fourth greyness curve for said second row;
measuring a distance D 2 , said distance D 2 being equal to the number of pixels between a first pixel in said first row having a second pre-selected greyness value from said third greyness curve and a second pixel in said second row having said second pre-selected greyness value from said fourth greyness curve; and
calculating said angle R 2 according to the following formula: π/2−arctan(D 2 /d 2 ), wherein d 2 is the number of pixels separating said first row and said second row.