Is a qr code unique?

Is a qr code unique?

QR codes are unique, and even if the content of the QR codes is the same, each generated QR code will have a different pattern. This is because the generation process uses data encryption and hashing techniques to ensure the uniqueness of each QR code.

Can Two Different QR Codes be The Same?

The answer is: almost impossible.

QR codes are composed of a matrix of black and white squares that convert information into a visual pattern through encoding techniques. During the generation process, a unique pattern is created based on the input data, selected error correction level, version information, and other parameters. The design of QR code generation algorithms aims to avoid collision issues (i.e., two different QR codes generating the same pattern). While there is a theoretical possibility of collision due to algorithm limitations, the likelihood is extremely low and can be disregarded. The design of QR codes incorporates increased data density and multiple error correction levels, further reducing the probability of collisions and ensuring that each QR code is unique.

The Uniqueness of QR Codes

The uniqueness of QR codes means that each QR code pattern should be one of a kind and reliably represent the encoded information. Uniqueness is crucial for QR code applications because it ensures the accuracy and security of information transmission. If QR codes were not unique, different QR code patterns might point to the same information, or the same QR code pattern might point to different information, causing data confusion and security risks.

Technologies Ensuring the Uniqueness of QR Codes

1. Data Encoding

The QR code generation process begins with data encoding, which converts information into machine-readable binary data. Standards like ISO/IEC 18004 define the format and encoding methods for QR codes. Different input data will produce different encoding results, generating unique QR code patterns.

2. Hash Algorithms

Hash algorithms process input data to produce fixed-length hash values. Even minor differences in hash values will result in completely different QR code patterns, ensuring uniqueness. Common hash algorithms include MD5, SHA-1, and SHA-256.

3. Encryption Techniques

Encryption techniques further secure the data and ensure the uniqueness of QR codes. By encrypting the data, it prevents tampering during transmission and guarantees that each generated QR code is unique.

4. Error Correction Levels

QR codes come with multiple error correction levels (such as L, M, Q, H). These levels not only enhance readability when the QR code is damaged or smudged but also increase data redundancy to further ensure the uniqueness of the QR code.

Uniqueness of QR Codes in Various Application Scenarios

application of QR codes in logistics and supply chain management

The uniqueness of QR codes is vital in numerous application scenarios. Here are a few typical examples:

1. Logistics and Supply Chain Management

In logistics and supply chain management, QR codes are used to track products from production to delivery. Unique QR codes ensure that each product has an independent tracking record, preventing confusion and counterfeit products.

2. Payment and Ticketing Systems

QR codes are widely used in payment and electronic ticketing systems. Unique QR codes ensure the independence and security of each transaction or electronic ticket, preventing duplicate payments or ticket fraud.

3. Digital Identity Verification

When QR codes are used for digital identity verification, their uniqueness guarantees that each verification request is distinct. By scanning the QR code, the system can quickly and accurately verify the user's identity, preventing identity theft and fraud.

4. Medical and Health Records

In the medical field, QR codes are used to manage medical records and health information. Unique QR codes ensure that each medical record is distinct and private, making it easy for medical personnel to quickly retrieve and update patient information.

Frequently Asked Questions

Can you reuse the same QR code?

Yes, dynamic QR codes allow the content to be modified after the QR code is generated, while the pattern remains unchanged. This means you can reuse the same QR code pattern. For example, in schools, teachers can distribute a QR code to students for accessing daily assignments. The next day, the teacher can update the content without redistributing the QR code. For students, they simply scan the same QR code to get the updated information. Reusing the same QR code can be practical in many scenarios.

Can Someone Change My QR Code?

Others cannot modify the data encoded in the QR code itself, as QR codes are read-only for users. However, there is an exception. For example, if you create a link QR code pointing to a website, the content seen by users when they scan the code can change if the website administrator updates the site. This might give the impression that the QR code content has changed, but it is actually the linked webpage content (including websites, Facebook, YouTube pages, etc.) that has been updated.

Can You Scan the Same QR Code Twice?

Generally, the same QR code can be scanned multiple times. However, there are cases where the QR code creator sets it to be scanned only once. This is rare, so whether a QR code can be scanned multiple times depends on the specific setting. Static QR codes have no limit on the number of scans (technically, it is impossible to limit the number of scans for static QR codes). For dynamic QR codes, it depends on the settings. In most cases, the same QR code can be scanned multiple times, even infinitely.

How Many Different QR Codes are Possible?

This is an interesting question, and we can make a simple calculation. For the smallest scale, a 21x21 matrix (simulating a QR code), this matrix consists of 441 squares (21 by 21). Each square can be black or white (recorded as 1 or 0 in a computer). If we randomly fill each square with black or white, there are 2 to the power of 441 possible combinations, roughly 56 trillion different patterns. This is for the smallest QR code pattern. As the scale of the QR code increases, the number of different patterns that can be generated grows exponentially.


  • International Organization for Standardization. (2015). ISO/IEC 18004:2015: Information technology — Automatic identification and data capture techniques — QR Code bar code symbology specification.
  • Eastlake, D., & Jones, P. (2001). RFC 3174 - US Secure Hash Algorithm 1 (SHA1). Retrieved from
  • Rivest, R. (1992). RFC 1321 - The MD5 Message-Digest Algorithm. Retrieved from
  • Eastlake, D., & Hansen, T. (2006). RFC 4634 - US Secure Hash Algorithms (SHA and SHA-based HMAC and HKDF). Retrieved from