A stack of a stack of currency bills is received, transported, and imaged. Image data reproducible as a visually readable image of one or more portions of at least one side of each currency bill in the stack is obtained. A serial number and at least one or more additional characters are extracted from the image data for each currency bill. A processor compares the extracted serial number and corresponding extracted one or more additional characters with stored serial number information and corresponding stored additional character information associated with the serial number information of genuine currency bills. The stored serial number information and corresponding stored additional character information uniquely identify a genuine currency bill. Any currency bill that does not have one or more extracted additional characters matching the stored serial number information and corresponding stored additional character information is flagged.