The concept for SurfSafe grew out of an earlier tool called BotCheck.me, developed by Bhat and Phadte’s startup, RoBhat Labs. It was also a browser extension that added a button to every Tweet and Twitter profile, which users could click to check whether that account likely belonged to a bot. Bhat and Phadte used machine learning to analyze the difference between typical bot behavior and human behavior on Twitter, and developed a model that they said could predict bots with over 93.5 percent accuracy.

Over the course of that work, the two students realized not only how much photo-based content these bots were sharing, but also just how difficult it was to vet. That’s a challenge afflicting both researchers and platforms, says Onur Varol, a postdoctoral researcher at Northeastern University's Center for Complex Network Research, who has helped build a competitor to BotCheck.me called Botometer. “Image fakery or trying to create misleading information in photos is a much deeper problem,” says Varol. “It’s a really difficult task even for journalists to validate if they’re fake or real.”

That's especially true, Varol says, when the image itself is real, but is presented online in an entirely different context. A photo from one protest, for instance, might turn up in a story about another, misleading the viewer about what really happened.

SurfSafe isn’t a perfect solution, but it’s certainly an ambitious start. It stores a unique digital fingerprint for every photo on more than 100 news sites that SurfSafe considers trusted, including outlets like NYTimes.com, CNN.com, and FoxNews.com. It also saves a signature of every photo its users see while they’re browsing the internet with the plug-in installed. “One user can see hundreds or thousands of images per day, just with basic browsing habits,” Phadte says.1 Photos that are similar but doctored will have fingerprints, or "hashes," that are almost, but not precisely, the same. "If an image is Photoshopped, only part of the image hash is different, so ultimately, we can tell that these images are pretty similar," Phadte says.

When a user hovers over a photo, SurfSafe scans the entire database of fingerprints to see if it’s ever encountered that image before in its raw or doctored form. If it has, it instantly surfaces the other images on the right side of the screen, prioritizing the earliest instance of the image, as it’s most likely to be the original. Users then have the ability to flag the image as either propaganda, Photoshopped, or misleading, which helps inform the SurfSafe model going forward.

Bhat acknowledges the tool has some blind spots. If SurfSafe has never encountered an image before, for instance, the user will simply see that there are no matches, even if that image is, in fact, fake. But Bhat views that as a minor flaw. “The fake news we care about is the fake news that’s spreading virally,” he says. “If a piece of fake news is spreading, we’ll have seen it.”

The more people who use SurfSafe, the more images the tool will ingest. If SurfSafe can get a few hundred thousand users in its first year, Bhat says he expects to have a database of 100 billion fingerprints.

Varol views this as a valuable starting point, because it saves people—professional fact-checkers included—a step. “This tool might capture the easy aspects of fact-checking, so you don’t have to go through the image and do your own background check,” he says.

Still, there are limitations that remain out of Bhat and Phadte’s control, the biggest of which is getting people to install the plug-in in the first place. After all, it’s partly a lack of digital literacy that makes people vulnerable to fake news. It’s a bit of a leap to expect someone whose main window to the internet is Facebook to take the additional step of installing a fact-checking plug-in. Another challenge is the fact that right now, the plug-in is only available on Chrome, Firefox, and Opera web browsers. That means SurfSafe can't flag content people find on their phones when they're inside an app, like Facebook. RoBhat Labs is working on a mobile version of the tool.