When there’s something in a photo that you’d like to keep personal, like a credit card number or someone’s face, you can blur or doodle over it. But that’s actually not a safe way to redact information, here’s why.
Why Blur Isn’t Good Enough Anymore
People have been erasing sensitive information on screenshots and photos for a long time. It is even used quite a bit in the news and other forms of media. However, as technology advances, it becomes much easier to decipher blurry and pixelated images. So what is the problem?
Blurring or scribbling on something is indeed a great way to hide sensitive information from human eyes, but that’s not what you should be worried about. Machine learning tools have made it relatively easy to get around simple redaction methods like blurring and pixelization.
Researchers at the University of Texas and Cornell University applied a simple deep learning algorithm to the task of identifying blurry faces. While humans had a paltry 0.19% accuracy, the algorithm was an incredible 71% accurate: 83% when given five tries. That is quite alarming.
Tools like this have been around for a while – the above study was from 2016—and they’re not particularly difficult to use. Similar tools have been trained to identify blurry faces with YouTube’s built-in video tools. All you need is open source software and a bunch of blurry photos to train it.
It’s not hard to see how this same technology can be used on even more sensitive information like credit card numbers, license plates, social security numbers, and much more. Fooling humans is easy enough, but fooling machine algorithms is another story.
Avoid These Writing Practices
Granted, blurring or pixelating text and photos isn’t good for sensitive information, but there’s more to it than that. Sometimes scribbling things also raises security concerns. We can see the case Microsoft vs. FTC as a perfect example.
Sony’s PlayStation CEO provided confidential documents with a bunch of numbers, dates and figures crossed out with black Sharpie. However, when those documents were scanned, it was quite easy to see the text under the marker. Now everyone can see the business details of Sony.
For the same reason, you should avoid simply using just one Sharpie, in both the physical and digital worlds. It’s relatively easy to see through Apple’s markup tool if the gamma is increased, and similar Android tools suffer from the same thing.
blur and doodle darkens information, but does not completely block it. And in the case of digital tools, sometimes it just creates a layer on top of the image, which could be removed if you’re not careful.
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the best method
The best way to truly cover up sensitive information is to make sure no trace is left behind. This requires more effort on your part, but it pays off when you hide sensitive information.
For example, check out this image of an Apple Card with the name blurred out. You can’t read it, but there is information in there that could be used by a machine learning tool to figure out what’s hidden under the pixelation. Because remember, technically speaking, I didn’t delete anything, I just rearranged the data.
Compare that to this image, which has the name completely blocked out by a solid bar of color. There is nothing there that can be used to rebuild what is below.
Finally, there is one additional crucial thing to consider. When redacting information from an image or document, you need to ensure that the technique you are using produces actual redaction and not just a mask.
If whatever format you’re working in, whether it’s an image file or a document file, supports layers and continuous editing, then you may run into issues where you put a solid color bar over sensitive information. Someone can turn around and lift that bar like someone removing masking tape from a canvas.
This is a historical and ongoing issue significant enough that tools like Adobe Acrobat and Preview have dedicated redaction tools that delete and overwrite redacted data to prevent the issue. So whatever tool you use, double check that it can’t flip and open the save file again and look under the compose bar.
This is what to aim for when hiding sensitive information. Think more about how you can delete more than dark. If you’re trying to hedge something in the physical world, don’t be afraid to double down. Pull out a good old Wite-Out and A marker.
Sensitive information is, well, sensitiveso don’t take a shortcut when it comes to hiding it, and always double check the method you used to compose it.