After experimenting with different forms of encryption, they filed a patent application, which was registered in 1952, even though they were still struggling to design a mechanism to read the code. They sold the patent soon afterwards. By the early 1970s, when American retailers and consumer-goods manufacturers began a program to design an industry-wide product identification system, the patent had expired. But Mr. Woodland’s employer, I.B.M., was involved with the project and assigned him to it. Mr. Silver had died in 1963.

At 8.01 a.m. on June 26, 1974, a packet of Wrigley’s Juicy Fruit chewing gum was sold for 67 cents at a Marsh Supermarket in Troy, Ohio — the first commercial transaction to use a bar code. More than five billion bar-coded products are now scanned at checkouts worldwide every day. Some of those codes will also have been vetted on the cellphones of shoppers who wanted to check the product’s impact on their health and the environment, and the ethical credentials of the manufacturer. They do so by photographing the bar code with their phones and using an application to access information about the product on ethical rating Web sites like GoodGuide.

As for the QR code, it was developed in the mid-1990s by the Japanese carmaker Toyota to track components during the manufacturing process. A mosaic of tiny black squares on a white background, the QR code has greater storage capacity than the original bar code. Soon, Japanese cellphone makers were adding QR readers to camera phones, and people were using them to download text, films and Web links from QR codes on magazines, newspapers, billboards and packaging. The mosaic codes then appeared in other countries and are now common all over the world. Anyone who has downloaded a QR reading application can decrypt them with a camera phone.

The value of both the original bar code and its brattish offspring is vested in the information they communicate, not the ciphers themselves. Yet anything that becomes as ubiquitous as those monochrome symbols has an effect on our surroundings, regardless of whether we consciously notice them.