Augmented reality

QR codes are used in some augmented reality systems to determine the positions of objects in 3-dimensional space.^[10]

Mobile operating systems

QR codes can be used on various mobile device operating systems. Both Android and iOS devices can natively scan QR codes without downloading an external app.^[35] The camera app is able to scan and display the kind of QR code along with the link . These devices support URL redirection, which allows QR codes to send metadata to existing applications on the device. Many free apps are available with the ability to scan the codes and hard-link to an external URL.

Virtual stores

QR codes have been used to establish "virtual stores", where a gallery of product information and QR codes is presented to the customer, e.g. on a train station wall. The customers scan the QR codes, and the products are delivered to their homes. This use started in South Korea,^[36] and Argentina,^[37] but is currently expanding globally.^[38] Walmart, Procter & Gamble and Woolworths have already adopted the Virtual Store concept.^[39]

QR code payment

QR codes can be used to store bank account information or credit card information, or they can be specifically designed to work with particular payment provider applications. There are several trial applications of QR code payments across the world.^[40][41] In developing countries including China,^[42][43] India^[44] and Bangladesh QR code payment is a very popular and convenient method of making payments. Since Alipay designed a QR code payment method in 2011,^[45] mobile payment has been quickly adopted in China. As of 2018, around 83% of all payments were made via mobile payment.^[46]

In November 2012, QR code payments were deployed on a larger scale in the Czech Republic when an open format for payment information exchange – a Short Payment Descriptor – was introduced and endorsed by the Czech Banking Association as the official local solution for QR payments.^[47][48] In 2013, the European Payment Council provided guidelines for the EPC QR code enabling SCT initiation within the Eurozone.

In 2017, Singapore created a taskforce including government agencies such as the Monetary Authority of Singapore and Infocomm Media Development Authority to spearhead a system for e-payments using standardized QR code specifications. These specific dimensions are specialized for Singapore.^[49]

The e-payment system, Singapore Quick Response Code (SGQR), essentially merges various QR codes into one label that can be used by both parties in the payment system. This allows for various banking apps to facilitate payments between multiple customers and a merchant that displays the single QR code. The SGQR scheme is co-owned by MAS and IMDA.^[50] A single SDQR label contains e-payments and combines multiple payment options. People making purchases can scan the code and see which payment options the merchant accepts.^[50]

Website login

QR codes can be used to log into websites: a QR code is shown on the login page on a computer screen, and when a registered user scans it with a verified smartphone, they will automatically be logged in. Authentication is performed by the smartphone, which contacts the server. Google developed this in 2012.^[51]

Mobile ticket

There is a system whereby a QR code can be displayed on a device such as a smartphone and used as an admission ticket.^[52][53] Its use is common for J1 League and Nippon Professional Baseball tickets in Japan.^[54][55] In some cases, rights can be transferred via the Internet. In Latvia, QR codes can be scanned in Riga public transport to validate Rīgas Satiksme e-tickets.^[56]

A sign with a QR code that links to a drinks menu

Restaurant ordering

Restaurants can present a QR code near the front door or at the table allowing guests to view an online menu, or even redirect them to an online ordering website or app, allowing them to order and/or possibly pay for their meal without having to use a cashier or waiter. QR codes can also link to daily or weekly specials that are not printed on the standardized menus,^[57] and enable the establishment to update the entire menu without needing to print copies. At table-serve restaurants, QR codes enable guests to order and pay for their meals without a waiter involved – the QR code contains the table number so servers know where to bring the food.^[58] This application has grown especially since the need for social distancing during the 2020 COVID-19 pandemic prompted reduced contact between service staff and customers.^[58]

Joining a Wi‑Fi network

A QR code to automatically join a Wi‑Fi network

By specifying the SSID, encryption type, password/passphrase, and if the SSID is hidden or not, mobile device users can quickly scan and join networks without having to manually enter the data.^[59] A MeCard-like format is supported by Android and iOS 11+.^[60]

• Common format: WIFI:S:<SSID>;T:<WEP|WPA|nopass>;P:<PASSWORD>;H:<true|false|blank>;;
• Sample: WIFI:S:MySSID;T:WPA;P:MyPassW0rd;;

Funerary use

QR code tile next to the grave of Wing Commander Adrian Warburton at Durnbach War Cemetery in Gmund am Tegernsee, Germany. The code links to his Wikipedia entry.

A QR code can link to an obituary and can be placed on a headstone. In 2008, Ishinokoe in Yamanashi Prefecture, Japan began to sell tombstones with QR codes produced by IT DeSign, where the code leads to a virtual grave site of the deceased.^[61][62][63] Other companies, such as Wisconsin-based Interactive Headstones, have also begun implementing QR codes into tombstones.^[64] In 2014, the Jewish Cemetery of La Paz in Uruguay began implementing QR codes for tombstones.^[65]

Electronic authentication

QR codes can be used to generate time-based one-time passwords (TOTP) for electronic authentication.

Loyalty programs

QR codes have been used by various retail outlets that have loyalty programs. Sometimes these programs are accessed with an app that is loaded onto a phone and includes a process triggered by a QR code scan. The QR codes for loyalty programs tend to be found printed on the receipt for a purchase or on the products themselves. Users in these schemes collect award points by scanning a code.

Counterfeit detection

Serialised QR codes have been used by brands^[66] and governments^[67] to let consumers, retailers and distributors verify the authenticity of the products and help with detecting counterfeit products, as part of a brand protection program.^[68] However, the security level of a regular QR code is limited since QR codes printed on original products are easily reproduced on fake products, even though the analysis of data generated as a result of QR code scanning can be used to detect counterfeiting and illicit activity.^[69] A higher security level can be attained by embedding a digital watermark or copy detection pattern into the image of the QR code. This makes the QR code more secure against counterfeiting attempts; products that display a code which is counterfeit, although valid as a QR code, can be detected by scanning the secure QR code with the appropriate app.^[70]

The treaty regulating apostilles (documents bearing a seal of authenticity), has been updated to allow the issuance of digital apostilles by countries; a digital apostille is a PDF document with a cryptographic signature containing a QR code for a canonical URL of the original document, allowing users to verify the apostille from a printed version of the document.

Product tracing

Different studies have been made to assess the effectiveness of QR codes as a means of conveying labelling information and their use as part of a food traceability system. In a field experiment, it was found that when provided free access to a smartphone with QR code scanning app, 52.6% of participants would use it to access labelling information.^[71] A study made in South Korea showed that consumers appreciate QR code used in food traceability system, as they provide detailed information about food, as well as information that helps them in their purchasing decision.^[72] If QR codes are serialised, consumers can access a web page showing the supply chain for each ingredient, as well as information specific to each related batch, including meat processors and manufacturers, which helps address the concerns they have about the origin of their food.^[73]

COVID-19 pandemic

Two QR codes that link to German contact tracing app check-ins during the COVID-19 pandemic

After the COVID-19 pandemic began spreading, QR codes began to be used as a "touchless" system to display information, show menus, or provide updated consumer information, especially in the hospitality industry. Restaurants replaced paper or laminated plastic menus with QR code decals on the table, which opened an online version of the menu. This prevented the need to dispose of single-use paper menus, or institute cleaning and sanitizing procedures for permanent menus after each use.^[74] Local television stations have also begun to utilize codes on local newscasts to allow viewers quicker access to stories or information involving the pandemic, including testing and immunization scheduling websites, or for links within stories mentioned in the newscasts overall.

In Australia, patrons were required to scan QR codes at shops, clubs, supermarkets and other service and retail establishments on entry to assist contact tracing. Singapore, Taiwan, the United Kingdom and New Zealand used similar systems.^[75]

QR codes are also present on COVID-19 vaccination certificates in places such as Canada and the EU (EU Digital COVID certificate), where they can be scanned to verify the information on the certificate.^[76]

Information capacity

The amount of data that can be represented by a QR code symbol depends on the data type (mode, or input character set), version (1, ..., 40, indicating the overall dimensions of the symbol, i.e. 4 × version number + 17 dots on each side), and error correction level. The maximum storage capacities occur for version 40 and error correction level L (low), denoted by 40-L:^[12][77]

Here are some samples of QR codes:

• 
  Version 1 (21×21). Content: "Ver1"
• 
  Version 2 (25×25). Content: "Version 2"
• 
  Version 3 (29×29). Content: "Version 3 QR Code"
• 
  Version 4 (33×33). Content: "Version 4 QR Code, up to 50 char"
• 
  Version 10 (57×57). Content: "VERSION 10 QR CODE, UP TO 174 CHAR AT H LEVEL, WITH 57X57 MODULES AND PLENTY OF ERROR CORRECTION TO GO AROUND. NOTE THAT THERE ARE ADDITIONAL TRACKING BOXES" (actually encoded in all capital letters). (Tracking boxes are more commonly called alignment patterns.)
• 
  Version 25 (117×117) Content: 1,269 characters of ASCII text describing QR codes
• 
  Version 40 (177×177) Content: "Version 40 QR Code can contain up to 1852 chars ..." (and followed by four paragraphs of ASCII text describing QR codes). The text refers to a QR Code with a "Level H" error correction. Other levels provide higher capacity.

Error correction

Damaged but still decodable QR code, link to http://en.m.wikipedia.org

Example of a QR code with artistic embellishment that will still scan correctly thanks to error correction

QR codes use Reed–Solomon error correction over the finite field ${\displaystyle \mathbb {F} _{256}}$, the elements of which are encoded as bytes of 8 bits; the byte ${\displaystyle b_{7}b_{6}b_{5}b_{4}b_{3}b_{2}b_{1}b_{0}}$ with a standard numerical value ${\displaystyle \textstyle \sum _{i=0}^{7}b_{i}2^{i}}$ encodes the field element ${\displaystyle \textstyle \sum _{i=0}^{7}b_{i}\alpha ^{i}}$ where ${\displaystyle \alpha \in \mathbb {F} _{256}}$ is taken to be a primitive element satisfying ${\displaystyle \alpha ^{8}+\alpha ^{4}+\alpha ^{3}+\alpha ^{2}+1=0}$. The primitive polynomial is ${\displaystyle x^{8}+x^{4}+x^{3}+x^{2}+1}$, corresponding to the polynomial number 285, with initial root = 0.

The Reed–Solomon code uses one of 37 different polynomials over ${\displaystyle \mathbb {F} _{256}}$, with degrees ranging from 7 to 68, depending on how many error correction bytes the code adds. It is implied by the form of Reed–Solomon used (systematic BCH view) that these polynomials are all on the form ${\textstyle \prod _{i=0}^{n-1}(x-\alpha ^{i})}$, however the rules for selecting the degree ${\displaystyle n}$ are specific to the QR standard.

When discussing the Reed–Solomon code phase there is some risk for confusion, in that the QR ISO/IEC standard uses the term codeword for the elements of ${\displaystyle \mathbb {F} _{256}}$, which with respect to the Reed–Solomon code are symbols, whereas it uses the term block for what with respect to the Reed–Solomon code are the codewords. The number of data versus error correction bytes within each block depends on (i) the version (side length) of the QR symbol and (ii) the error correction level, of which there are four. The higher the error correction level, the less storage capacity. The following table lists the approximate error correction capability at each of the four levels:

In larger QR symbols, the message is broken up into several Reed–Solomon code blocks. The block size is chosen so that no attempt is made at correcting more than 15 errors per block; this limits the complexity of the decoding algorithm. The code blocks are then interleaved together, making it less likely that localized damage to a QR symbol will overwhelm the capacity of any single block.

Due to error correction, it is possible to create artistic QR codes with embellishments to make them more readable or attractive to the human eye, and to incorporate colors, logos, and other features into the QR code block; the embellishments are treated as errors, but the codes still scan correctly.^[79][80]

It is also possible to design artistic QR codes without reducing the error correction capacity by manipulating the underlying mathematical constructs.^[81][82] Image processing algorithms are also used to reduce errors in QR-code.^[83]

Encoding

The format information records two things: the error correction level and the mask pattern used for the symbol. Masking is used to break up patterns in the data area that might confuse a scanner, such as large blank areas or misleading features that look like the locator marks. The mask patterns are defined on a grid that is repeated as necessary to cover the whole symbol. Modules corresponding to the dark areas of the mask are inverted. The format information is protected from errors with a BCH code, and two complete copies are included in each QR symbol.^[3]

The message dataset is placed from right to left in a zigzag pattern, as shown below. In larger symbols, this is complicated by the presence of the alignment patterns and the use of multiple interleaved error-correction blocks.

• 
  Meaning of format information. In the above figure, the format information is protected by a (15,5) BCH code, which can correct up to 3 bit errors. The total length of the code is 15 bits, of which 5 are data bits (2 EC level + 3 mask pattern) and 10 are extra bits for error correction. The format mask for these 15 bits is: [101010000010010]. Note that we map the masked values directly to its meaning here, in contrast to image 4 "Levels & Masks" where the mask pattern numbers are the result of putting the 3rd to 5th mask bit, [101], over the 3rd to 5th format info bit of the QR code.
• 
  Message placement within a Ver 1 QR symbol (21×21). The message is encoded using a (255,248) Reed Solomon code (shortened to (26,19) code by using "padding") that can correct up to 2 byte-errors. A total of 26 code-words consist of 7 error-correction bytes, and 17 data bytes, in addition to the "Len" (8 bit field) "Enc" (4 bit field), and "End" (4 bit field).
• 
  Larger symbol (Ver 3) illustrating interleaved blocks. The message has 26 data bytes and is encoded using two Reed-Solomon code blocks. Each block is a (255,233) Reed Solomon code (shortened to (35,13) code), which can correct up to 11 byte-errors in a single burst, containing 13 data bytes and 22 "parity" bytes appended to the data bytes. The two 35-byte Reed-Solomon code blocks are interleaved so it can correct up to 22 byte-errors in a single burst (resulting in a total of 70 code bytes). The symbol achieves level H error correction.

The general structure of a QR encoding is as a sequence of 4 bit indicators with payload length dependent on the indicator mode (e.g. byte encoding payload length is dependent on the first byte).^[84]

Four-bit indicators are used to select the encoding mode and convey other information.

Encoding modes can be mixed as needed within a QR symbol. (e.g., a url with a long string of alphanumeric characters )

[ Mode Indicator][ Mode bitstream ] --> [ Mode Indicator][ Mode bitstream ] --> etc... --> [ 0000 End of message (Terminator) ]

After every indicator that selects an encoding mode is a length field that tells how many characters are encoded in that mode. The number of bits in the length field depends on the encoding and the symbol version.

Alphanumeric encoding mode stores a message more compactly than the byte mode can, but cannot store lower-case letters and has only a limited selection of punctuation marks, which are sufficient for rudimentary web addresses. Two characters are coded in an 11-bit value by this formula:

V = 45 × C₁ + C₂

This has the exception that the last character in an alphanumeric string with an odd length is read as a 6-bit value instead.

Decoding example

The following images offer more information about the QR code.

• 
  1 – Introduction
• 
  2 – Structure
• 
  3 – Layout & Encoding
• 
  4 – Levels & Masks
• 
  5 – Protocols

Model 1

Model 1 QR code is an older version of the specification. It is visually similar to the widely seen model 2 codes, but lacks alignment patterns. Differences are in the bottom right corner, and in the midsections of the bottom and right edges are additional functional regions.

• 
  Model 1 QR code example
• 
  Model 1 QR code functional regions

Micro QR code

Micro QR code is a smaller version of the QR code standard for applications where symbol size is limited. There are four different versions (sizes) of Micro QR codes: the smallest is 11×11 modules; the largest can hold 35 numeric characters,^[85] or 21 ASCII alphanumeric characters, or 15 bytes (128 bits).

• 
  Micro QR code example
• 
  Micro QR code functional regions

iQR code

iQR code is an alternative to existing square QR codes developed by Denso Wave. iQR codes can be created in square or rectangular formations; this is intended for situations where a longer and narrower rectangular shape is more suitable, such as on cylindrical objects. iQR codes can fit the same amount of information in 30% less space. There are 61 versions of square iQR codes, and 15 versions of rectangular codes. For squares, the minimum size is 9 × 9 modules; rectangles have a minimum of 19 × 5 modules. iQR codes add error correction level S, which allows for 50% error correction.^[86] iQR Codes had not been given an ISO/IEC specification as of 2015, and only proprietary Denso Wave products could create or read iQR codes.^[87]

• 
  iQR code example

Secure QR code

Secure Quick Response (SQR) code is a QR code that contains a "private data" segment after the terminator instead of the specified filler bytes "ec 11".^[88] This private data segment must be deciphered with an encryption key. This can be used to store private information and to manage a company's internal information.^[89]

Frame QR

Sample of a Frame QR that encodes a text message saying "This is a specimen for the Wikimedia Foundation".

This shows how FrameQR can combine both the code and the image together and that the frame doesn't have to be square but could be a circle as well.

Frame QR is a QR code with a "canvas area" that can be flexibly used. In the center of this code is the canvas area, where graphics, letters, and more can be flexibly arranged, making it possible to lay out the code without losing the design of illustrations, photos, etc.^[90]

HCC2D

Samples of the High Capacity Colored 2-Dimensional (HCC2D) code: (a) 4-color HCC2D code and (b) 8-color HCC2D code.

Researchers have proposed a new High Capacity Colored 2-Dimensional (HCC2D) Code, which builds upon a QR code basis for preserving the QR robustness to distortions and uses colors for increasing data density (as of 2014 it is still in prototyping phase). The HCC2D code specification is described in details in Querini et al. (2014),^[91] while techniques for color classification of HCC2D code cells are described in detail in Querini and Italiano (2014),^[92] which is an extended version of Querini and Italiano (2013).^[93]

Introducing colors into QR codes requires addressing additional issues. In particular, during QR code reading only the brightness information is taken into account, while HCC2D codes have to cope with chromatic distortions during the decoding phase. In order to ensure adaptation to chromatic distortions that arise in each scanned code, HCC2D codes make use of an additional field: the Color Palette Pattern. This is because color cells of a Color Palette Pattern are supposed to be distorted in the same way as color cells of the Encoding Region. Replicated color palettes are used for training machine learning classifiers.