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 checking for N×N crosses of two crossing lines in said non-dilated first and second pixel blobs in which one of the lines of the N×N cross in said non-dilated first pixel blob has a different color from the other line of the corresponding N×N cross in said non-dilated second pixel blob, wherein N is a number of bits.