Patent ID: 7438231

Claim:
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.