A bill to be verified is scanned lengthwise by a two track optical sensor. For each bill the resulting analog signals are divided into eight segments or windows each segment producing a binary coded pattern produced by delta modulation. This is compared to a stored reference and a number is produced representing the dissimilarity between the bill being scanned and the average bill of that denomination with which it is being compared. Thereafter, a processor compares the foregoing numbers with additional quantitative functions which have previously been stored relating the corresponding segments of the bill denomination being scanned to other bill denominations. With the use of limit and weighting functions they are summed over the eight different effective windows and a decision is made as to whether the proper denomination is present.