Among them, ISBN is the international standard book number, and it is an identification code consisting of 13 digits, which can usually be found on the back or back cover of a book. This number can be used to identify and classify books, which is convenient for bookstore and library management.

Another bar code may be used to identify the price, which contains the price information of books, so that bookstores and consumers can quickly identify the price. The barcode can also contain other relevant information, such as publication date, printing date, etc.

In a word, the two bar codes at the back of each book may be set for the convenience of managing and tracking book information.