Canvas Fingerprinting: Protect Your Privacy

TL;DR

Your web browser’s canvas element can be used to create a unique fingerprint, potentially tracking you across websites. This isn’t typical cookie-based tracking, but it’s more subtle and harder to block. You can reduce the risk by disabling canvas or using privacy-focused browsers/extensions.

What is Canvas Fingerprinting?

Websites use JavaScript to draw something hidden on a ‘canvas’ element in your browser. The way your computer renders this image – even slightly different due to your hardware, operating system, fonts, and browser settings – creates a unique ‘fingerprint’. This fingerprint can be used to identify you, even if you clear cookies or use a VPN.

How Does it Work?

1. JavaScript Code: A website runs JavaScript code that draws an image on the canvas.
2. Rendering Differences: Your computer’s graphics card, browser version, fonts, and other factors affect how the image is drawn.
3. Data Extraction: The JavaScript reads the pixel data of the rendered image.
4. Fingerprint Creation: This pixel data is converted into a hash (a unique string of characters). Even small differences in rendering produce different hashes.
5. Tracking: Websites can store this hash and use it to identify you on future visits, even without cookies.

How to Protect Yourself

Completely preventing canvas fingerprinting is difficult, but here are several steps you can take:

1. Browser Settings & Extensions

1. Privacy-Focused Browsers: Use browsers designed with privacy in mind, such as Brave or Tor Browser. These often have built-in canvas fingerprinting protection.
2. Browser Extensions: Install extensions like Privacy Badger, uBlock Origin (with advanced settings enabled), or CanvasBlocker.

• Privacy Badger: Automatically learns to block trackers, including those using canvas fingerprinting.
• uBlock Origin: A powerful ad and tracker blocker; configure it to specifically block canvas fingerprinting scripts (advanced settings).
• CanvasBlocker: Specifically designed to prevent canvas fingerprinting by blocking or randomizing the canvas data.

2. Disable Canvas (Advanced)

Disabling canvas entirely will break some websites, but it’s the most effective way to stop canvas fingerprinting.

1. Firefox: Type about:config in the address bar and press Enter. Search for canvas.fingerprinting.enabled and set it to false.
2. Chrome/Edge (via Flags): Type chrome://flags/#disable-canvas-fingerprinting in the address bar and enable the flag ‘Disable canvas fingerprinting’. Note: flags can change or disappear with browser updates.

3. Randomize Canvas Data

Some extensions attempt to randomize the canvas data, making it harder to create a consistent fingerprint.

4. Use NoScript (Advanced)

NoScript blocks JavaScript by default, giving you control over which scripts run on each website. This prevents canvas fingerprinting but requires more manual configuration.

5. Regularly Clear Browser Data

1. Clear your browser’s cache, cookies, and site data regularly. While this doesn’t directly stop canvas fingerprinting, it reduces the amount of information available to trackers.

Checking if You Are Fingerprinted

You can use websites like AmiUnique or BrowserLeaks Canvas Test to see how unique your browser fingerprint is.

Important Considerations

• False Positives: Some anti-tracking tools may incorrectly identify legitimate website functionality as tracking.
• Website Compatibility: Disabling canvas or blocking scripts can break some websites.
• Ongoing Battle: Tracking techniques are constantly evolving, so staying informed and updating your privacy measures is crucial.