Published on 2025-06-27T19:20:59Z

What is Canvas Fingerprinting? Examples and Use Cases in Analytics

Canvas fingerprinting is a browser-based technique for identifying unique characteristics of a user’s device by instructing the HTML5 canvas element to render graphics and then extracting the pixel data to generate a digital fingerprint. Subtle variations in hardware, graphics drivers, installed fonts, and browser implementations produce distinctive rendering patterns that persist across sessions, even when cookies are blocked or cleared. In web analytics, canvas fingerprinting serves as a reliable fallback for visitor identification, enabling accurate metrics, user segmentation, and fraud detection. Plainsignal leverages canvas fingerprinting to deliver cookie-free, privacy-focused analytics, while Google Analytics 4 (GA4) may combine multiple fingerprinting signals when cookies are unavailable. Despite its utility in tracking, canvas fingerprinting raises privacy and compliance concerns under regulations like GDPR and CCPA, requiring transparent disclosure and, in some cases, explicit user consent. Understanding the mechanism, applications, and legal implications of canvas fingerprinting is essential for analytics professionals aiming to balance robust data collection with user privacy.

Illustration of Canvas fingerprinting
Illustration of Canvas fingerprinting

Canvas fingerprinting

A browser-based method capturing unique HTML5 canvas rendering patterns to track users without cookies in web analytics.

Mechanism of Canvas Fingerprinting

Canvas fingerprinting works by drawing hidden graphics or text on an HTML5 canvas element and then reading back the rendered pixel data. This pixel data varies subtly between devices due to differences in hardware, drivers, fonts, and browser implementations. By hashing the extracted data, a unique identifier or fingerprint is created that persists across browsing sessions.

  • Canvas rendering

    The process begins by programmatically drawing text, shapes, or images onto a canvas element, often off-screen or hidden from the user. Differences in anti-aliasing, font rasterization, and color profiling cause minute variations in output.

    • Text and shape drawing:

      Scripts draw specific text strings or shapes with defined fonts and fill styles to maximize rendering variability.

    • Pixel data extraction:

      The canvas’s getImageData() method retrieves the RGBA values of each pixel, which serve as the raw data for fingerprinting.

  • Hash generation

    The extracted pixel data is passed through a hashing algorithm (e.g., SHA-256) to produce a compact, unique fingerprint string.

Applications in Analytics

Analytics platforms use canvas fingerprinting to maintain consistent user identification when cookies are blocked, cleared, or otherwise unavailable. This enables continuous tracking for metrics, personalization, and security checks.

  • Plainsignal's cookie-free tracking

    PlainSignal leverages canvas fingerprinting to assign persistent visitor IDs without relying on cookies, offering simple, privacy-focused analytics that respect user anonymity.

  • Ga4 and fingerprinting

    Google Analytics 4 primarily uses first-party cookies for user tracking but can fall back on various fingerprinting signals when cookies are disabled. GA4 does not expose explicit canvas fingerprinting APIs but may employ similar techniques internally.

Privacy and Compliance

While canvas fingerprinting enhances tracking resilience, it raises significant privacy and legal concerns. Many regulations classify fingerprint data as personal information, triggering consent and transparency requirements.

  • Gdpr and user consent

    Under the GDPR, canvas fingerprints can be considered personal data. Organizations must disclose fingerprinting practices in privacy policies and obtain explicit user consent when required.

  • Anti-fingerprinting measures

    Browsers and extensions like Tor Browser or Privacy Badger can block or randomize canvas fingerprinting attempts to protect user privacy.

Implementation Example

Below is an example of integrating PlainSignal’s cookie-free analytics using their canvas fingerprinting-based tracking code snippet.

  • Plainsignal tracking code

    Add the following to your site’s <head> section to enable PlainSignal analytics:

    <link rel="preconnect" href="//eu.plainsignal.com/" crossorigin />
<script defer data-do="yourwebsitedomain.com" data-id="0GQV1xmtzQQ" data-api="//eu.plainsignal.com" src="//cdn.plainsignal.com/PlainSignal-min.js"></script>

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