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> Years ago it would've required a supercomputer and a PhD to do this stuff This isn't actually true. You could do this 20 years ago on a consumer laptop, and

> Years ago it would've required a supercomputer and a PhD to do this stuff This isn't actually true. You could do this 20 years ago on a consumer laptop, and you don't need the information you get for free from text moving under a filter either. What you need is the ability to reproduce the conditions the image was generated and pixelated/blurred under. If the pixel radius only encompasses, say, 4 characters, then you only need to search for those 4 characters first. And then you can proceed to the next few characters represented under the next pixelated block. You can think of pixelation as a bad hash which is very easy to find a preimage for. No motion necessary. No AI necessary. No machine learning necessary. The hard part is recreating the environment though, and AI just means you can skip having that effort and know-how.

cogman10 2y ago
In fact, there was a famous de-censoring that happened because the censoring which happened was a simple "whirlpool" algorithm that was very easy to unwind. If media companies want to actually censor something, nothing does better than a simple black box.
- lynndotpy 2y ago
  Ah yes, Mr. Swirl Face. This was pretty different though. The decensoring algorithm I'm describing is just a linear search. But pixelation is not an invertible transformation. Mr. Swirl Face just applied a swirl to his face, which is invertible (-ish, with some data lost), and could naively be reversed. (I am pretty sure someone on 4chan did it before the authorities did, but this might just be an Internet Legend).
  - Modified3019 2y ago
    A long while ago, taking an image (typically porn), scrambling a portion of it, and having others try to figure out how to undo the scrambling was a game played on various chans.
  - cjbgkagh 2y ago
    Christopher Paul Neil is a real person who went to jail.
    - Der_Einzige 2y ago
      Shhhhh!!!!! Yeah but if you read about him it serves as a rallying cry for right wing types since he's an example of the candaian legal systems extreme leniency. This guy should be in prison forever and he's been free since 2017. Look at his record of sentencing. I love being a bleeding heart liberal/progressive and all, but this is too far. Furthermore, don't look too hard at Isreal and it's policy of being very, very open to pedophiles and similar types.
- rcfox 2y ago
  > nothing does better than a simple black box You still need to be aware of the context that you're censoring in. Just adding black boxes over text in a PDF will hide the text on the screen, but might still allow the text to be extracted from the file.
  - falcor84 2y ago
    Indeed. And famously, using black boxes as a background on individual words in a non-monospaced font is also susceptible to a dictionary attack on an image of the widths of the black boxes.
    - lesuorac 2y ago
      And even taking sharpie and drawing a black box doesn't mean the words can be seen at a certain angle or by removing the sharpie ink but not the printed ink. Really, if you need to censor something create a duplicate without the originals. Preferably literally without the originals as the size of the black box is also an information leak.
    - snotrockets 2y ago
      No need for the monospaced requirement - it would reduce the search space, but it's solvable even before this reduction.
      - fc417fc802 2y ago
        The additional leakage provided by non-monospace is rather large. With monospace all you know is the character count.
  - Voultapher 2y ago
    Curious anyone know if the specific censoring tool in the MacOS viewer has this problem? I had assumed not because they warn you when using the draw shapes tool that text below it can be recovered later and they don't warn you about that when using the censoring tool.
- benatkin 2y ago
  A completely opaque shape or emoji does it. A simple black box overlay is not recommended unless you that’s the look you’re going for. Also very slightly transparent overlays come in all shapes and colors and are hard to recognize whether it’s a black box or another shape, so either way you need to be careful it’s 100% opaque.
thehappypm 2y ago
this gets exponentially harder with a bigger blur radius, though.
- deleted 2y ago
  [deleted]
nartho 2y ago
Noob here, can you elaborate on this ? if you take for example a square of 25px and change the value of each individual pixels to the average color of the group, most of the data is lost, no ? if the group of pixels are big enough can you still undo it ?
- DougMerritt 2y ago
  It's not that you're utterly wrong; some transformations are irreversible, or close to. Multiplying each pixel's value by 0, assuming the result is exactly 0, is a particularly clear example. But others are reversible because the information is not lost. The details vary per transformation, and sometimes it depends on the transformation having been an imperfectly implemented one. Other times it's just that data is moved around and reduced by some reversible multiplicative factor. And so on.
- its-summertime 2y ago
  How many pixels are in `I` vs how many are in `W`? different averages as a result. With subpixel rendering, kerning, etc, there is minute differences between the averages of `IW` and `WI` as well, order can be observed. It is almost completely based on having so much extra knowledge: the background of the text, the color of the text, the text renderer, the font, etc, there are a massive amount of unknowns if it is a random picture, but if we have all this extra knowledge, it massively cuts down on the amount of things we need to try: if its 4 characters, we can make a list of all possibilities, do the same mosaic, and find the closest match, in nearly no time.
- porphyra 2y ago
  Yeah most of the information is lost, but if you know the font used for the text (as is the case with a screencast of a macOS window), then you can try every possible combination of characters, render it, and then apply the averaging, and see which ones produce the same averaged color that you see. In addition, in practice not every set of characters is equally likely --- it's much more likely for a folder to be called "documents" than "MljDQRBO4Gg". So that further narrows down the amount of trying you have to do. You are right, of course, that the bigger the group of pixels, the harder it gets: exponentially so.
BoingBoomTschak 2y ago
Something like https://github.com/Jaded-Encoding-Thaumaturgy/vapoursynth-descale https://github.com/Jaded-Encoding-Thaumaturgy/vapoursynth-de..., you mean?

cogman10 2y ago

In fact, there was a famous de-censoring that happened because the censoring which happened was a simple "whirlpool" algorithm that was very easy to unwind. If media companies want to actually censor something, nothing does better than a simple black box.

lynndotpy 2y ago
Ah yes, Mr. Swirl Face. This was pretty different though. The decensoring algorithm I'm describing is just a linear search. But pixelation is not an invertible transformation. Mr. Swirl Face just applied a swirl to his face, which is invertible (-ish, with some data lost), and could naively be reversed. (I am pretty sure someone on 4chan did it before the authorities did, but this might just be an Internet Legend).
- Modified3019 2y ago
  A long while ago, taking an image (typically porn), scrambling a portion of it, and having others try to figure out how to undo the scrambling was a game played on various chans.
- cjbgkagh 2y ago
  Christopher Paul Neil is a real person who went to jail.
  - Der_Einzige 2y ago
    Shhhhh!!!!! Yeah but if you read about him it serves as a rallying cry for right wing types since he's an example of the candaian legal systems extreme leniency. This guy should be in prison forever and he's been free since 2017. Look at his record of sentencing. I love being a bleeding heart liberal/progressive and all, but this is too far. Furthermore, don't look too hard at Isreal and it's policy of being very, very open to pedophiles and similar types.
rcfox 2y ago
> nothing does better than a simple black box You still need to be aware of the context that you're censoring in. Just adding black boxes over text in a PDF will hide the text on the screen, but might still allow the text to be extracted from the file.
- falcor84 2y ago
  Indeed. And famously, using black boxes as a background on individual words in a non-monospaced font is also susceptible to a dictionary attack on an image of the widths of the black boxes.
  - lesuorac 2y ago
    And even taking sharpie and drawing a black box doesn't mean the words can be seen at a certain angle or by removing the sharpie ink but not the printed ink. Really, if you need to censor something create a duplicate without the originals. Preferably literally without the originals as the size of the black box is also an information leak.
  - snotrockets 2y ago
    No need for the monospaced requirement - it would reduce the search space, but it's solvable even before this reduction.
    - fc417fc802 2y ago
      The additional leakage provided by non-monospace is rather large. With monospace all you know is the character count.
- Voultapher 2y ago
  Curious anyone know if the specific censoring tool in the MacOS viewer has this problem? I had assumed not because they warn you when using the draw shapes tool that text below it can be recovered later and they don't warn you about that when using the censoring tool.
benatkin 2y ago
A completely opaque shape or emoji does it. A simple black box overlay is not recommended unless you that’s the look you’re going for. Also very slightly transparent overlays come in all shapes and colors and are hard to recognize whether it’s a black box or another shape, so either way you need to be careful it’s 100% opaque.

thehappypm 2y ago

this gets exponentially harder with a bigger blur radius, though.

deleted 2y ago
[deleted]

nartho 2y ago

Noob here, can you elaborate on this ? if you take for example a square of 25px and change the value of each individual pixels to the average color of the group, most of the data is lost, no ? if the group of pixels are big enough can you still undo it ?

DougMerritt 2y ago
It's not that you're utterly wrong; some transformations are irreversible, or close to. Multiplying each pixel's value by 0, assuming the result is exactly 0, is a particularly clear example. But others are reversible because the information is not lost. The details vary per transformation, and sometimes it depends on the transformation having been an imperfectly implemented one. Other times it's just that data is moved around and reduced by some reversible multiplicative factor. And so on.
its-summertime 2y ago
How many pixels are in `I` vs how many are in `W`? different averages as a result. With subpixel rendering, kerning, etc, there is minute differences between the averages of `IW` and `WI` as well, order can be observed. It is almost completely based on having so much extra knowledge: the background of the text, the color of the text, the text renderer, the font, etc, there are a massive amount of unknowns if it is a random picture, but if we have all this extra knowledge, it massively cuts down on the amount of things we need to try: if its 4 characters, we can make a list of all possibilities, do the same mosaic, and find the closest match, in nearly no time.
porphyra 2y ago
Yeah most of the information is lost, but if you know the font used for the text (as is the case with a screencast of a macOS window), then you can try every possible combination of characters, render it, and then apply the averaging, and see which ones produce the same averaged color that you see. In addition, in practice not every set of characters is equally likely --- it's much more likely for a folder to be called "documents" than "MljDQRBO4Gg". So that further narrows down the amount of trying you have to do. You are right, of course, that the bigger the group of pixels, the harder it gets: exponentially so.

BoingBoomTschak 2y ago

Something like https://github.com/Jaded-Encoding-Thaumaturgy/vapoursynth-descale https://github.com/Jaded-Encoding-Thaumaturgy/vapoursynth-de..., you mean?