5 ms·

I suspect there's not much information in the individual blurred face, but I wonder if given enough examples you'd be able to determine if an unblurred face is

I suspect there's not much information in the individual blurred face, but I wonder if given enough examples you'd be able to determine if an unblurred face is the one in a sample of images with any level of confidence? You can do that with text (http://dheera.net/projects/blur http://dheera.net/projects/blur).

KingOfCoders 6y ago
The number of different characters is quite limited. Does this work for Chinese or only for Latin type languages?
Arnt 6y ago
The face and its surroundings are blurred almost to a single colour. The average RGB value of my face might be unique-ish, but if you mix in some variable background, photographed on a camera whose lens has been smeared against the pocket of someone's jeans, the result should be human, not individual. A side comment: AFAICT what the Signal developers have done is take code that was developed so that the phone camera could autofocus on faces, and and used that code to defocus faces. What a sweet hack.
- TheCraiggers 6y ago
  > "The face and its surroundings are blurred almost to a single colour." To your eyes, maybe. To a machine, you have an array of pixels, each with different values which, using an algorithm, could be adjusted into something your eyes can resolve into a unique face.
  - Arnt 6y ago
    Seriously? Look at https://www.androidpolice.com/wp-content/uploads/2020/06/04/signal-face-blur-b.png https://www.androidpolice.com/wp-content/uploads/2020/06/04/... — do you really think there's enough information in those two rectangles to reconstruct the faces even approximately?
    - TheCraiggers 6y ago
      Hard to tell, I'm not a computer; but it does look better than most. To be fair (to me), I was basing my critique on the picture in TFA, which seems to have far more detail in it. That said, the whole point of my post was that humans are really bad at judging this. Many blur algorithms can be reversed because they just modify the color values of the pixels in a reversible way. You can't always tell by looking at a picture what data is still there, in much the same way you can't see the stars in an ISO 200 picture of the night sky. It's not until you open it in GIMP and crank the exposure up to max that you see just how much data is there that your eyes couldn't perceive.
    - bigiain 6y ago
      I kinda hope there's not only enough information there to algorithmically reverse, but that when you do that - all the de-blurred faces end up being George Floyd.
- hnarn 6y ago
  A very sweet hack, but I think the concern was based on the example image provided in the link posted. While the face is blurred, there's still a lot of information you can glean about the person: their haircut, their neck, the clothes worn etc. -- so I'm guessing the threat vector here is that if you also have a general set of pictures from the same demo, you may be able to automatically identify who the blurred person is. Blurring is better than nothing but the best picture when it comes to avoid being traced is the picture that was never taken.
  - Arnt 6y ago
    Yes. Someone who has access to many photos of the same set of people might well able to identify people on one photo, even though their faces are blurred on that particular one. I'm not sure whether the large number of photos nowadays is a net negative, though. That's also what finally stopped Derek Chauvin.
  - lm28469 6y ago
    Let's be real for 2 seconds here, this is pure nonsense. No court of law would do anything about "hey we arrested that guy because he has 2 eyes, a mouth and the same tshirt as that other guy who was protesting yesterday", if it comes to this you wouldn't even need a picture of blurred faces, just arrest whoever you want and provide forged evidences (or none) because that's exactly the same thing And even then law enforcement are already filming them (cctv + from the air) and tracking their phones, the last thing you have to worry about is a 100% blurred face that no amount of technical power would be able to process or match back to you.
    - fragmede 6y ago
      picture A of an individual, unblurred, protesting peacefully. picture B of a blurred individual from later on in the same protest, wearing the exact same clothes, commiting questionable acts, is circumstantially incriminating.
    - TremendousJudge 6y ago
      bikeshedding? on hacker news? no way

KingOfCoders 6y ago

The number of different characters is quite limited. Does this work for Chinese or only for Latin type languages?

Arnt 6y ago

The face and its surroundings are blurred almost to a single colour. The average RGB value of my face might be unique-ish, but if you mix in some variable background, photographed on a camera whose lens has been smeared against the pocket of someone's jeans, the result should be human, not individual. A side comment: AFAICT what the Signal developers have done is take code that was developed so that the phone camera could autofocus on faces, and and used that code to defocus faces. What a sweet hack.

TheCraiggers 6y ago
> "The face and its surroundings are blurred almost to a single colour." To your eyes, maybe. To a machine, you have an array of pixels, each with different values which, using an algorithm, could be adjusted into something your eyes can resolve into a unique face.
- Arnt 6y ago
  Seriously? Look at https://www.androidpolice.com/wp-content/uploads/2020/06/04/signal-face-blur-b.png https://www.androidpolice.com/wp-content/uploads/2020/06/04/... — do you really think there's enough information in those two rectangles to reconstruct the faces even approximately?
  - TheCraiggers 6y ago
    Hard to tell, I'm not a computer; but it does look better than most. To be fair (to me), I was basing my critique on the picture in TFA, which seems to have far more detail in it. That said, the whole point of my post was that humans are really bad at judging this. Many blur algorithms can be reversed because they just modify the color values of the pixels in a reversible way. You can't always tell by looking at a picture what data is still there, in much the same way you can't see the stars in an ISO 200 picture of the night sky. It's not until you open it in GIMP and crank the exposure up to max that you see just how much data is there that your eyes couldn't perceive.
  - bigiain 6y ago
    I kinda hope there's not only enough information there to algorithmically reverse, but that when you do that - all the de-blurred faces end up being George Floyd.
hnarn 6y ago
A very sweet hack, but I think the concern was based on the example image provided in the link posted. While the face is blurred, there's still a lot of information you can glean about the person: their haircut, their neck, the clothes worn etc. -- so I'm guessing the threat vector here is that if you also have a general set of pictures from the same demo, you may be able to automatically identify who the blurred person is. Blurring is better than nothing but the best picture when it comes to avoid being traced is the picture that was never taken.
- Arnt 6y ago
  Yes. Someone who has access to many photos of the same set of people might well able to identify people on one photo, even though their faces are blurred on that particular one. I'm not sure whether the large number of photos nowadays is a net negative, though. That's also what finally stopped Derek Chauvin.
- lm28469 6y ago
  Let's be real for 2 seconds here, this is pure nonsense. No court of law would do anything about "hey we arrested that guy because he has 2 eyes, a mouth and the same tshirt as that other guy who was protesting yesterday", if it comes to this you wouldn't even need a picture of blurred faces, just arrest whoever you want and provide forged evidences (or none) because that's exactly the same thing And even then law enforcement are already filming them (cctv + from the air) and tracking their phones, the last thing you have to worry about is a 100% blurred face that no amount of technical power would be able to process or match back to you.
  - fragmede 6y ago
    picture A of an individual, unblurred, protesting peacefully. picture B of a blurred individual from later on in the same protest, wearing the exact same clothes, commiting questionable acts, is circumstantially incriminating.
  - TremendousJudge 6y ago
    bikeshedding? on hacker news? no way