Pixelating or blurring doesn’t actually work to hide text

If you’ve ever pixelated an email address or blurred a phone number before putting an image onto the internet in order to protect someone’s privacy, I’ve got bad news for you: Researchers at the University of California-San Diego have found that the popular Photoshop redaction techniques are decodable such that the underlying text can be read.

The researchers were able to recover text from a variety of redacted screenshots that they found online, said computer science professor Hovav Shacham by email. They were, for example, able to figure out the blurred email address in this screenshot of a conversation between a corrupt DEA agent and the then-CEO of Bitcoin exchange Mt. Gox.

It’s not the first time we’ve discovered that a Photoshop redaction tool doesn’t work as well as thought. In 2007, we found out that Photoshop’s “twirly” filter was reversible. A man had posted pornographic photos of himself with young boys to the internet, “twirling” his face to protect his identity, but was busted when Interpol untwirled his photo.

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