1. A method for comparing in a binary image a first pixel blob with a second pixel blob to determine whether they represent matching symbols, comprising the steps of: a) dilating the first blob and checking if the second blob fits inside the dilated first blob, b) dilating the second blob and checking if the first blob fits inside the dilated second blob, c) if said steps a) and b) result in a match, checking whether said match is erroneous or not by checking if the non-dilated first pixel blob contains a line not present in the non-dilated second pixel blob and vice versa, wherein said step c) comprises directly comparing corresponding sets of N×N crosses of two crossing lines in said non-dilated first and second pixel blobs, wherein each corresponding set of N×N crosses comprises a first N×N cross considered on said non-dilated first pixel blob and a second N×N cross considered on said non-dilated second pixel blob in the same position, and declaring an erroneous match if for at least one of said sets one of the two crossing lines of the first N×N cross has a different color from the other line of the two crossing lines of the second N×N cross, wherein N is a number of bits.