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Comment by cabirum | Hacker News Reader

To extract the noise from sensor imperfections, wouldn't one need unaltered images in raw format?

Automatic denoise and image compression ought to erase all but most obvious defects.

A lifetime ago, I summarized the techniques of sensor detection for a stackoverflow answer, see [1].

The generic answer is every step of the acquisition/storage process can create artifacts worth analyzing statistically: lens defects, color filter array patterns, imaging sensor noise, color filter array interpolation technique, JPEG quantization coefficient varying per camera/manufacturers...

[1]: https://stackoverflow.com/a/33674103/4576325

From reading the article, it looks like it talsk about PRNU[0] without really saying it's PRNU. For a while this technique was known (the earliest papers about it are from the early 2000s) but it was computationally complex at the moment, and the domain of a few very knowledgeable persons. A couple[1] of years ago, MobilEdit finally included a decent UI and implementation of the technique into their software[2], which has made it available. However, I'm unsure if the majority of those who use it truly understand what the technique does and what conclusions you can draw from it.

Oh and great summary on SO FrenchyJiby! It's a good intro to those that aren't aware of what can and can't be done in image analysis :)

[0] https://forensicnerd.wordpress.com/techniques/image-forensic...

[1] https://xkcd.com/1070/

[2] https://www.mobiledit.com/camera-ballistics-features

Call me cynical but I've noticed an uptick in phony police capability stories like these that I expect make parallel construction easier.

Yes, but it sounds like forensic researchers envision this tool being the equivalent to bullet striation. So in other words, law enforcement finds a suspect, captures their camera, photographs RAW images, and then compares the sensor imperfections in the seized camera to known illicit materials.

Of course this breaks down with used sales and camera rentals, especially since those aren’t tracked as intensively as firearms sales.

And breaks down if they're not doing enough to have good statistics on false matches. That's one of the classic problems with DNA evidence.

It’s possibly difficult with one or two images but with several, I’m pretty sure you can apply some sort pattern matching and statistically hit a certainty threshold. The question then becomes, can you use this tech as forensic evidence in a court?

Guessing that with several compressed images you can recover the original sensor noise pattern.

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