Canvas fingerprinting, the tracking tool you can’t get away from

Going online without being tracked is getting harder and harder.


Micah Singleton


Published Jul 22, 2014   Updated May 30, 2021, 10:14 pm CDT

If you thought cookies were the only thing tracking you around the Internet, think again. First reported by ProPublica, researchers at Princeton University and KU Leuven University have discovered a new tracking tool called canvas fingerprinting; it’s a tracking tool that appears on 5 percent of the top 100,000 sites and is nearly impossible to get away from.

For years companies have sought to track users across the Internet, mainly with cookies, to map out your interests and browsing habits to determine which ads you are most likely to click on. The problem with that plan is cookies can be easily erased on any browser, which in most cases will make the ads shown to you unappealing to your interests. 

This leads to a situation where most ads are either annoying or bad, and people just want to get rid of them, which is why the use of ad-blocking software is rising. AdBlock has over 20 million users on Chrome and Safari. AdBlock Plus (a different company) has been downloaded over 300 million times, and currently has over 28 million active users on Chrome and Firefox. 

With so many people blocking ads, companies and advertisers have been looking for a better way to find out what you like and dislike, what you look at on the Internet, and what you would be interested in buying to serve better ads that you may actually click on.

Canvas fingerprinting instructs your Web browser to draw a specific image, which is hidden from you (ProPublica can show you what it looks like) . Because every computer has different settings—different software, clock settings, fonts, etc.—every image drawn is unique. Just like cookies, canvas fingerprints build a profile of you as you traverse the Internet, which determines what ads you come across. Canvas fingerprinting isn’t being used by everyone, but it is utilized by AddThis, a social media and ad-sharing company whose tools appear on 14 million sites worldwide. 

Speaking to ProPublica, AddThis CEO Rich Harris said despite concerns about privacy, canvas fingerprinting is “well within the rules and regulations and laws and policies that we have.” Harris noted that canvas fingerprinting has only been rolled out to a small portion of the sites AddThis is available on and that the company is considering ending the test, as it considers canvas fingerprinting to not be “uniquely identifying enough.” 

Harris said data collected via canvas fingerprinting is only being used for internal research and development, and if you don’t want your information used for ad targeting, you can add an opt-out cookie to your browser. (What better way to stop being tracked by cookies than another cookie?)

Unlike cookies, canvas fingerprinting is extremely difficult to block. Your browser can’t block them natively, and extensions like AdBlock won’t do the trick either. Outside of using Tor—which recently added a feature that alerts you when sites try to use canvas fingerprinting, and sends a blank page in its place—there is no simple way to avoid canvas fingerprinting.

We have asked Microsoft (Internet Explorer), Google (Chrome), Mozilla (Firefox), and Apple (Safari) about adding features to the browsers that can block or opt-out of canvas fingerprinting but have not yet received responses.

Update: Microsoft declined to comment.

H/T ProPublica Photo via Alan Levine/Flickr (CC BY-SA 2.0)

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*First Published: Jul 22, 2014, 12:20 pm CDT