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Comment by excalibur | Hacker News Reader

So... colored boxes over faces > fancier methods?

Well, you have to ask yourself - how much information remains in the image after I apply this method?

Is the state of the obfuscated image still related somehow to the state of the non-obfuscated version? If yes, your obfuscation method sucks.

You need to change the image in such a way that the state of the obfuscated part after you apply the method is not related in any way to its state before. Otherwise clever algorithms will always find a way to "leak" info out of your poor choice of method.

The best thing is to just drop a black (#000000) blob over the relevant part, completely replacing the part snd deleting previous bits 100%. There's no information leak other than size then.

Blurring algos, pixelation, all that fancy stuff from the movies looks good on screen but is naive in practice.

Of course, if you use a "smart" file format that has undo history and such, then you might still be leaking info.

One of the authors here. There was some great work from the Max-Planck Institute that came out recently which looked into this[0]. They examined images that used black or white boxes to cover faces and found that neural networks could pick up on cues like body posture and the surrounding environment to identify individuals.

[0] https://arxiv.org/abs/1607.08438

Yup. In 2004 Interpol busted a pedophile by untwirling his (lousy) face obfuscation: http://boingboing.net/2007/10/08/untwirling-photo-of.html

It's not even very difficult: just apply the same twirl transformation in the opposite direction.

Yes. For simple text-censoring examples de-pixelating is quite easy (since you know a lot about what could be under it), it was only a matter of time that somebody applied better tools to harder cases.

(you can of course cover something up with a random pixelated pattern if that looks less jarring, but it then is a purely cosmetic choice: the important bit is to remove all information connected to the obscured content)

The US government has known this forever. Ever see those black boxes over censored documents? It's obviously better than blurring, the only information you get is the size of the box.

> Ever see those black boxes over censored documents? It's obviously better than blurring, the only information you get is the size of the box.

Actually, quite a few times in the past with that method, you've gotten the complete text, because someone uses a format that includes the text as text (like PDF) and then dropped a solid-black box over the text, which looks like the text is obliterated, but preserves the entire content in the file.

One time in college. A teacher did something like this with hw and solutions being "hidden"/"censored". And I was easily able to get around it and have all the solutions :/

One of our lecturers did something similar, but with class grades. They started from a complete list of grades in Excel, and for each student, deleted all grades but that student's grades and then saved a copy.

Unfortunately, they did this without disabling the Excel feature that saved undo data in the file, so anyone in the class was able to hit Ctrl+Z a couple of times and see the entire list of grades.

Which, depending on the font, can be enough to reverse-enginner the text, particularly if there is a smallish list of options.

Of course, if you block out a whole line, then things get much, much harder, basically impossible. There are many possible lines!

sounds like it. though, i think for aesthetic purposes, i'd prefer a random or "stock" obfuscated faces rather than a colored box.

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