in Production
The barcode on the back of a book
The barcode on a book is neither decoration nor optional. It encodes the ISBN, and it has to scan first time.
Almost every book sold through bookshops carries a barcode on the back cover. It is there so the book can be scanned at the till, in the warehouse and in the library. It is not decorative, and a barcode that will not scan causes problems for everyone who handles the book.
What the barcode encodes
A book's barcode is an EAN-13 barcode, the same symbol used on retail products internationally. For books, it encodes the 13-digit ISBN.
Every ISBN-13 begins with a prefix, 978 or 979, which identifies the item as a book within the EAN system. Older ISBNs had ten digits, and they convert to thirteen by adding 978 at the front and recalculating the final digit. That final digit is always a check digit, calculated from the others, which lets a scanner detect most misreads.
The digits printed beneath the bars should match the ISBN on the copyright page. If they do not, something has gone wrong.
One ISBN per format
Each format of a book needs its own ISBN, and so its own barcode. The hardback, the paperback and the audiobook each have separate ISBNs. An ebook usually has its own too, though it does not need a printed barcode. A new edition with substantial changes also needs a new ISBN.
This matters for the barcode because the wrong ISBN, or one ISBN shared between two formats, means the book is recorded as the wrong product every time it is scanned.
The price add-on
Some book barcodes carry a smaller second barcode to the right of the main one. This is a five-digit add-on that can encode a price, with the first digit indicating the currency. It is widely used in the United States, where the code 90000 means no price is encoded. Whether a book needs one depends on where it will be sold and what the retailers and distributors involved require.
Making it scan
Barcode generators, including some built into design software, produce the barcode from the ISBN. It is best supplied as vector artwork, so it stays sharp at any size.
A barcode has to meet some basic conditions to scan reliably. It should be printed in a dark colour, ideally black, on a white or very light background. Red bars, or bars on a red, dark or busy background, may not scan at all: many scanners read with red light, and red looks pale to them.
It needs clear space, known as the quiet zone, on either side of the bars. It should not be shrunk too far, stretched or distorted, and should not be placed across a fold or a curved edge.
The EAN-13 specification defines a nominal size and allows scaling only within limits. Shortening the height of the bars to save space is common on books, but it reduces the scanner's margin for error, so it is best done cautiously if at all.
The usual position is the lower part of the back cover, most often the bottom right. A white panel behind the barcode solves most background problems. It should sit well inside the safe zone so that trimming cannot clip it.
Finally, test it. A barcode-reading app on a phone is enough to confirm that the barcode on the printed proof scans and returns the right ISBN.