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Signal goes Gaussian to take privacy to the next level: All your faces don't belong to us

Blur tool brings privacy protection to images, in these troubled times

Amid nationwide protests over the death of George Floyd, secure comms biz Signal has deployed a blur tool in its messaging and calling app to allow users to obscure faces in app-captured snapshots.

"At Signal, we support the people who have gone into the streets to make their voices heard," wrote co-founder and CEO Moxie Marlinspike, in a blog post. "We believe that something in America needs to change, and even if we don’t know exactly how, we support and trust in the people who are self-organizing around the country to figure it out."

Marlinspike said many of the groups pushing for change have been using Signal to communicate. The group, he said, is working to deal with the surge of traffic and is looking for ways to support those demanding change.

"One immediate thing seems clear: 2020 is a pretty good year to cover your face," he said, in a nod to the coronavirus outbreak and the general difficulty of maintaining privacy in the camera-strewn panopticon of public space.

The coronavirus pandemic has complicated the aspirations of facial recognition firms and rendered high-tech surveillance countermeasures redundant. Where once activists like Adam Harvey explored geometric make-up patterns as a way to make faces unrecognizable to specific algorithms, his advice now is just wear a mask.

But since not everyone always does so, the latest versions of Signal for Android and iOS include a blur feature in the image editor menu that can be used to degrade image details.

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Tapping on the blur menu button allows you to draw over an image with a blurred stroke and loads a radio button atop the image that, when selected, automatically tries to find faces in the image to overlay them with a blurred box.

Marlinspike concedes the software isn't perfect and doesn't always properly detect faces. That's why manual blurring is also enabled.

Blurring should be thought of mainly as a privacy courtesy than as a serious security mechanism. Signal's blur tool may be worthwhile to de-identify distant faces captured in a crowd scene but it's unlikely to be enough to prevent a closeup in good lighting from being recognizable. What's more, blurring algorithms can potentially be reversed.

Obscuring an image feature with a solid block of color – doable with the pen tool but not very easily – is a stronger form of redaction. At least, Signal removes metadata from images.

Marlinspike said Signal also plans to distribute physical face coverings in the near future. Details, he said, will be provided soon.

As Facebook CEO Mark Zuckerberg declared at his company's F8 developer conference last year, despite ample evidence to the contrary, the future is private. ®

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