Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Image Scrubber: tool for anonymizing photographs taken at protests

everestpipkin.github.io

Post reply on HN
Print view View original

121–130 of 410 posts

Re: Image Scrubber: tool for anonymizing photographs taken at protests

#121

Post by pgalvin »

mceachen wrote: post #62
cowmix wrote: post #6

This is great for some situations. However, my personal policy is to upload my protest content to Google Photos asap (if appropriate). This makes sure your content is off your device if your phone gets confiscated AND it provides (be it thin) layer of authenticity/validation of the content.

Google Photos isn't going to provide you with any authenticity claims, and metadata gets scrambled by both their "high quality" and "original" settings. If you want to make sure the actual, original image gets stored safely on another device automatically, use SyncThing or Resilio Sync.

> metadata gets scrambled by both their "high quality" and "original" settings.

This is NOT true, at least for the "original" setting. Upload an image, download it again - the checksums are identical.

If you modify the time/date or add comments within Google Photos, that new information is kept in a .json file instead of the exif data, but Google NEVER modifies the original photo if you select "original" quality.

Re: Image Scrubber: tool for anonymizing photographs taken at protests

#122

Post by forgotmypw17 »

NightlyDev wrote: post #120
Ansil849 wrote: post #119

Some tips to maximise user privacy while deploying this tool: 1) The code, for now, runs locally. This is good. To avoid the possibility of the code being tampered with at a later day (for example, it could be modified to send copies of the image to a server), download the webpage and use the saved copy, not the live copy. 2) Do not use the blur functionality. For maximum privacy, this should be removed from the app…

"There are _a lot_ of forensic methods to reverse blur techniques" Any examples? You can't reverse it if the data is gone.

The data may still be there, it just looks like it's gone.

Re: Image Scrubber: tool for anonymizing photographs taken at protests

#123

Post by dqv »

MauranKilom wrote: post #110
siberianbear wrote: post #56

Earlier quoted context omitted.

That wasn't really a "blur", though. A swirl like that is just moving pixels around. If know how the algorithm works, you can reverse it. Probably, it was done with a common program like Adobe Photoshop or Gimp or something. One could write a program that would just "unswirl" with various parameters and generate a bunch of images, and a human could pick out the one that looks like an unswirled image. If you can pick…

> That can't be done with a blur. In a blur, pixels are merged or averaged together and information is lost. I'd be careful with that assumption. The only thing that really loses information is the discretization back into 0-255 range, and that naturally loses very little information. If you consider the pixels as a large vector of values, you're effectively multiplying it by a matrix (plus discretization afterwards)…

What about in the case of a mosaic blur?

Re: Image Scrubber: tool for anonymizing photographs taken at protests

#124

Post by Uehreka »

hangphyr wrote: post #106

The timing of the release of this tool seems a bit innapropriate, given the state of rioting in a few US cities now. It's going to be incredibly draining on law enforcement in the US for a few years to identify and prosecute criminals involved in riots. Most victims already who have lost their homes, their businesses, and even their loved ones will mostly likely never see the criminals brought to justice given the sc…

It would be nice if our law enforcement had legitimacy and credibility, because then we could know that showing someone’s face would lead to them being arrested and facing a sentence commensurate with what they had done. But unfortunately this is not the case.

Showing the face of a protestor smashing in a window will not lead to that protestor being brought to court and handed a sentence for community service, a fine, or some light jail time. It will lead to extrajudicial retaliation and possibly death.

Again, it would be nice if that weren’t the case and we could trust law enforcement to behave appropriately. But given that they and their supporters are known to hunt down and kill people who protest against them, we cannot in good conscience make it easier for them to do so.

If we are to trust the cops again, they need to show us they are worthy of trust. And they sure aren’t doing that right now.

Re: Image Scrubber: tool for anonymizing photographs taken at protests

#126

Post by enriquto »

MauranKilom wrote: post #118
enriquto wrote: post #27

Earlier quoted context omitted.

> How resilient is blurring against deconvolution? This depends a lot on the implementation details. If you blur an image using arbitrary-precision real numbers, then blurring is invertible. If you add a bit of random noise, or quantize your pixels into a finite-precision data type, then it becomes essentially one-way, and you cannot recover the original image.

> you cannot recover the original image Technically you are correct - you cannot recover the exact original image. The same is the true for saving an image as JPEG. But the question at hand is whether you can still recognize faces, not whether you can restore a byte-for-byte of the original. And whether JPEG or blurring, the answer is generally "yes". It does depend on the implementation (and whether you know the imp…

Yes, my point is that it depends a lot on the specific blurring. If you just average a square neighborhood of 4 pixels around the center, and add no noise, it is very likely that you can "enhance" the resolution back to almost the original image. Yet, if the blur kernel is much larger (say, a gaussian of width 40 pixels), and you add some noise after te blur, it is very likely that you have completely destroyed the information.

Re: Image Scrubber: tool for anonymizing photographs taken at protests

#127

Post by chrisseaton »

NightlyDev wrote: post #120
Ansil849 wrote: post #119

Some tips to maximise user privacy while deploying this tool: 1) The code, for now, runs locally. This is good. To avoid the possibility of the code being tampered with at a later day (for example, it could be modified to send copies of the image to a server), download the webpage and use the saved copy, not the live copy. 2) Do not use the blur functionality. For maximum privacy, this should be removed from the app…

"There are _a lot_ of forensic methods to reverse blur techniques" Any examples? You can't reverse it if the data is gone.

> You can't reverse it if the data is gone.

That's the problem - the data you think is gone isn't gone. High frequencies are gone.... but you left all the low frequencies, didn't you? You can read a face from the low frequencies.

Re: Image Scrubber: tool for anonymizing photographs taken at protests

#128

Post by okamiueru »

forgotmypw17 wrote: post #122
NightlyDev wrote: post #120

Earlier quoted context omitted.

"There are _a lot_ of forensic methods to reverse blur techniques" Any examples? You can't reverse it if the data is gone.

The data may still be there, it just looks like it's gone.

Blur is in effect a lowpass filter on the image. The high frequency information is gone. Reconstruction based on domain knowledge, like AI methods etc is unlikely to be able to reconstruct the distinguishing features between people enough to avoid false positives when used to search for similar people.

Then again, maybe groups of people can be associated together, and a poor match is good enough given other clues.

So, much better to be safe than sorry.

I'm not sure if I had a particular good point to make, other than that blurring does remove information that cannot easily be reversed. You can probably make very convincing reconstructions, but they might not look like the original person.

Re: Image Scrubber: tool for anonymizing photographs taken at protests

#129

Post by paulryanrogers »

augustt wrote: post #81
paulryanrogers wrote: post #79

Earlier quoted context omitted.

Is this meant to be sarcasm? (Honest question)

Yes - the actual phrase is "It is better that ten guilty persons escape than that one innocent suffer".

Thanks for clarifying for me.

Still, I would hope that as police are investigated they are held to a high standard of behavior. They do after all have a near monopoly on the lawful use of violence.

Re: Image Scrubber: tool for anonymizing photographs taken at protests

#130

Post by SiempreViernes »

wongarsu wrote: post #55
elliekelly wrote: post #16

Earlier quoted context omitted.

I’m reminded of a reddit thread a while back about the US government paying a large sum to create an “unblur” function for photoshop. Someone in the comments was able to rotate and flip a photo and use the photoshop blur tool to effectively undo a blur for free. Perhaps it’s better to remove the section of photo with a person’s face instead? Or draw a shape over their face and flatten the image? It seems to me as lon…

Blurring isn't that good at destroying information, I think we mostly use it because it's the best looking censoring attempt. I would pixelate the faces to be just 4x4 giant pixels. It destroys nearly as much information as blacking them out while still not disrupting the image too much

If final appearance is important, just blur a bunch of pictures of Trump and paste the appropriate one over the face. Or an unblurred face for that matter.
Post reply on HN