• by Wendy Davis , Staff Writer @wendyndavis, January 13, 2016

More tech companies than ever are using controversial "canvas fingerprinting" technology to track Web users.

That's according to Princeton University's Steven Englehardt, who recently ran new tests designed to uncover the technique. Englehardt was one of the authors of a 2014 report about canvas fingerprinting that called attention to the technique.

He says in a blog post that new tests show that the number of "distinct trackers" using canvas fingerprinting has doubled since 2014.

"In the absence of a lawsuit, policy change, or technical solution, we see that canvas fingerprinting use is beginning to grow again," he writes.

At the same time, he says that the code is present on fewer sites than in the past. Englehardt also suggests that those sites aren't as popular as the ones flagged in his 2014 study.

He attributes that dropoff in publishers to the bad publicity following his earlier report. "A tracker which is present on a large number of sites, or is present on sites which receive more traffic is more likely to be the focus of news articles or subject to lawsuits," he writes. "Indeed, our 2016 measurements support it: we’ve seen a large increase in the number of parties involved, but the increase is limited to parties with a much smaller presence."

Canvas fingerprinting code directs users' browsers to draw unique images, which are then used to identify those computers in the future, according to ProPublica, which first reported on the technology.

The tracking code identified by the researchers was written by several different tech companies, including social sharing company AddThis -- which was present on popular sites like Whitehouse.gov and YouTube. Overall, canvas-fingerprinting code was present on 5% of the 100,000 most popular sites in 2014.

The 2014 study drew worldwide attention and media coverage, triggering a privacy backlash. Around the same time the report was published, AddThis publicly said it disabled the tracking code.