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The fingerprint inside photos
- muterad_murilax 6y agoWas expecting this to be yet another article about EXIF data (only). Glad to learn something new!
- yaur 6y ago> So, even if you used two cameras of the same make and model to snap a uniformly lit surface – where every point on the surface has the same brightness – there'd be subtle differences unique to each camera. Ok, but will that survive JPEG compression? Since JPEG is meant to remove details that aren't visible to the human eye it would be surprising if this fingerprint survived in a usable way.
- Keirmot 6y agoAccording to the article: > Technically, it should be possible to suppress, for example, by reducing the image resolution, says Farid. But, by how much? This of course depends on many factors such as the type of device used for image capture, as well as the fingerprint matching algorithm employed. There is no one-size-fits-all solution to fingerprint removal.
- formerly_proven 6y agoThe effect is real, but cameras actively try to suppress it. Cameras have a map of particularly bad pixels which are ignored (much like a bad sector map in a hard drive), and when doing long exposures most cameras will/can do two exposures, where the second one is made with the shutter closed. I'm skeptical this works after boiling 24...50 megapixels down into a tiny web-sized image with 1-3 MP.
- kergonath 6y agoYes, it does survive compression. That’s why if you’re into astrophotography and want to stack pictures you start by taking a black picture. That way, you capture the noise pattern to remove from the noise from the other pictures.
- ant6n 6y agoWouldn't astrophotography be done using lossless (or no) compression?
- kergonath 6y agoIt depends. Cheap webcams are commonly used for planets, for example. They record a bunch of JPEGs or a movie, which are then processed and stacked. The idea is that with many exposures you get as much signal as with a long one, without the associated artefacts (noise from high sensitivity, blur from fluctuations in the atmosphere, etc). Compression artefacts don’t matter as much, but sensor noise does. Of course, in some cases shooting RAW from a specialised camera is better, but quite often JPEGs straight out of a standard (cheap DSLR or mirrorless, or webcam) camera are more than enough. Takes an order of magnitude less memory as well, which counts when you have stacks with 200 pictures. There is a discussion here, for example: https://www.planetguide.net/astrophotography-webcam/ https://www.planetguide.net/astrophotography-webcam/
- mikewarot 6y agoGetting rid of dark noise is one thing, the gain of each pixel is apparently a bit random due to manufacturing processes as well. You'd have to take a picture of a uniform white surface to calibrate that out as well.
- kergonath 6y agoYes, exactly. Except that we take a picture with no light at all to get an image of the noise from the sensor, typically leaving the lens cap on.
- EmilioMartinez 6y agoJPEG compression is calculated locally in small segments, so variations across the whole surface can still survive, each segment being independent. JPEG is not "meant" to remove detail, more like prioritize large-scale phenomena, which in this case would preserve imbalances between segments.
- dandanua 6y ago> In the post-truth age, the ability to spot fakery is obviously a positive development I like how they call the modern world. Though, I'm not sure what time in history can be called "truth age".
- lifthrasiir 6y agoMost of the history was "pre-truth age". By the intermediate value theorem there surely was a brief, infinitesimal period of "truth age". /jk I guess the word "post-truth" means the lack of truth as an objective or goal, not the lack of truth by itself.
- air7 6y ago> what time in history can be called "truth age". I'd say most of it, and we're still largely there. People basically believe what they're being told and shown. Being inhertinaly skeptical is very rare.
- EmilioMartinez 6y ago>post-truth age This sad term makes me feel like there are adults out there still grappling with the fact that lies and uncertainty exist
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- axguscbklp 6y agoWhy is it that cameras automatically add metadata to photos, anyway? If I go to buy a camera, what I expect it to do is take photos and that's it, not to add some data to the photos without asking me.
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- obeattie 6y agoWe have very different expectations. I'd be pretty annoyed if I couldn't browse and sort my photos by date taken.
- axguscbklp 6y agoThat makes sense. I myself would prefer to have to do something to get the camera to add a timestamp to a photo but I can understand that probably so many people want it to be the default that there's little reason for manufacturers to not make it the default.
- arendtio 6y agoBtw. it is not just about date and location. Many cameras also add the lens, aperture, exposure time and the like, which can be very useful for post-processing. I think most EXIF information isn't that sensitive. And regarding the timestamp: it isn't that accurate after all, because the timezone is 'local' (whatever that means). So if you don't know where the picture has been taken or can't be sure that the device actually uses the local timezone (who changes the time on his DSLR when he travels to a different timezone?), you can only derive the date with certainty. After all, whenever you post an image online you should be aware of the information you put out there. For example, if you are an American and in the background of the picture is the Eiffel Tower, a burglar doesn't have to be Sherlock Homes to guess that you are on vacation. In addition, the article is about the information that is not explicitly encoded into the image (like EXIF), but implicitly reveals the sensor fingerprint, which you would not see even if you would take a look at every byte in the file, because you need to know what exactly to look for. If you know what too look for, you could theoretically see it even on the printed version of the picture ;-)
- nextlevelwizard 6y agoWouldn't you need a reference picture to compare two cameras? Or would you be able to determine which camera took a specific picutre if you get hold of it and can take test pictures? Or can you just compare two completely separate pictures and determine if they are taken with the same camera? If you can then that means protestors/anarchists who intend on documenting what is going on and want to stay anonymos should buy a sort of "burner" camera that they do not use for anything else.
- hyko 6y agoThe first rule of hand wavy forensic pseudoscience club is that there are no rules, you just need to be able to bamboozle a jury.
- specialist 6y agoaka Agile Forensics
- kergonath 6y agoYou can analyse things like vignetting, distortion and chromatic aberration to identify a camera model or family. I suppose you could also look for details in AI-processed photos to try and identify the processing software, possibly down to the software version. It would work with phones, for example. Not with manually processed photos, though. The dark noise pattern is specific to each sensor, so if you can reliably get this, you could identify specific devices. So, there are caveats but you can get a lot of information. It's probably a good idea to use a common phone or cheap camera. And change date and time, and make sure it does not leak anything in the EXIF metadata. And make sure that the sensor does not have any dead pixel, because that would be a dead giveaway.
- ersinesen 6y ago[Shameless plug] This app removes that fingerprint (i.e. PRNU): https://www.esenbil.com/photoclean https://www.esenbil.com/photoclean
- hyko 6y agothis technology could also be used to reveal AI-generated synthetic imagery Yeah, AI may one day be able to fool the human visual system but it will never be able to add a watermark to a video.
- antirez 6y agoLOL, I don't understand what they were thinking when writing this part. AI may be used, probably, in order to remove the watermark even right now, not one day, but recognizing the non uniform part, subtracting it and adding a different one. To create the training set of same-image taken with differnt-sensor is not hard.
- elwell 6y agoIt's a game of cat and mouse of course.
- hyko 6y agoWhere the mouse is now the size of a horse. Ultimately this is a classic case of security through obscurity, it won’t protect us from deep fakes long term.
- aimor 6y agoI've seen a lot of attempts at neural network image generation that create constant artifacts in the images. It's not that image generators are unable to add a specific bias to their images in an attempt to look like a specific camera. It's the opposite: generators have their own signatures that these techniques can detect and track.
- hyko 6y agoThat part doesn’t really need ML of any kind; ultimately unless a watermark is based on a rigorous and proven cryptographic scheme, it can be faked. They are apparently not doing anything like that, it’s just “hey, these photo sites are all a bit different”. Well, that’s what they’re saying publicly anyway, could be complete bs and every sensor has a government sanctioned backdoor in it.
- tmabraham 6y agoIIRC, Facebook has a patent where photos taken with the same camera can be detected, which I think is similar to "photo response non-uniformity". They use it for recommending friends. I think there was a case where Facebook was recommending to friend request other people who all had their weddings taken by the same wedding photographer!
- msantos 6y agoYeah, I'm surprised that that didn't get a mention in the article. Here's a link to the patent: "Associating cameras with users and objects in a social networking system" https://patents.google.com/patent/US20150124107A1/en https://patents.google.com/patent/US20150124107A1/en
- Donckele 6y agoThis link should work: https://patents.google.com/patent/US20150124107A1/en https://patents.google.com/patent/US20150124107A1/en
- antirez 6y agoIn the article there is no mention that EXIF tags are stripped away by all the major social networks / messaging systems.
- whiterace1488 6y agoIt's there actually: >Some social media platforms remove information like geolocation (though only from public view), but many other websites do not.
- foobar33333 6y agoIts also important to know that just because they strip it for the public facing file, there is no reason they don't store it privately to comply with legal requests.
- te_chris 6y agoThey mention that they don’t publish them but surely keep them and analyse them themselves
- cyphar 6y agoThis reminds me of a technobabble fingerprinting technique in the (not very good) movie Beyond a Reasonable Doubt (2009). It has a pretty uncanny resemblance to the method the researcher created for detecting if a photo has been altered (the idea being that cameras have unique noise fingerprints and you can detect if some part of the image doesn't have the same fingerprint to cast doubt on the authenticity of the photo).
- the_pwner224 6y agoThis is a great article on detecting that a photo had been altered, also using things like noise fingerprints: (original seems to be down rn, here's the archive link): https://web.archive.org/web/20101229153120/http://www.hackerfactor.com/blog/index.php?/archives/322-Body-By-Victoria.html https://web.archive.org/web/20101229153120/http://www.hacker... And HN discussions, from 2009: https://news.ycombinator.com/item?id=1017726 https://news.ycombinator.com/item?id=1017726 and from 9 months ago: https://news.ycombinator.com/item?id=23538059 https://news.ycombinator.com/item?id=23538059
- unicornporn 6y agoexiftool -all= filename.ext That is all.
- justaj 6y agoSomeone didn't read the article...
- supernova87a 6y agoThis is why I always print out my photos and then fax them to Google to be uploaded to my albums.
- lazyweb 6y agoThat would likely unironically be a thing if Google were a german company.
- dsnr 6y agoThat would probably be the only way of doing it. And you would have to give Google a 3 months notice to remove a photograph from your album.
- kortex 6y agoSome fingerprints and/or editing artifacts survive this. Search for "rebroadcast attack".
- arendtio 6y agoActually, that is the first time I see the JPEG artifacts as something beneficial. Maybe they should invert the 'quality' scale and call it 'privacy' ;-)
- madaxe_again 6y agoIf cameras had a setup step similar to astrophotography systems, this wouldn’t be a thing. Dark frame to remove thermal noise, bias frame to remove noise in the ADC, and a flat frame to remove vignetting. I don’t actually see any of those as being difficult to implement - but I guess there’s also no market.
- londons_explore 6y agoIt's perhaps prudent to be very wary when using this technique. Errors in a CCD are not necessarily random - if the error is on a mask used in the silicon production process, you might find for example that hundreds of other sensors across the world all have a very similar error profile. Knowing if your software has picked up two images taken by the same camera, or one of the few hundred made with the same masks is going to be awfully hard to do with sufficient confidence...
- kortex 6y agoThis is exactly a technique used in media forensics. You can even tell things like crop region and lens geometry (due to subpixel statistics and chromatic aberration). Train a resnet on tens/hundreds of thousands of images and you'd be surprised what labels it can learn.
- 2Gkashmiri 6y agoIn 2014 when my city was innundated with floods and no electricity meant internet was hard, I tracked down a photo posted online using exif data to inform another person that the photo was of his neigbourhood and that the photo was taken at a particular time. I remember spending days/weeks 18 hours a day cold calling all my contacts one after the other because I wanted to "hear someone say they are alive". In the end everything worked out pretty fine and a major disaster didnt happen.
- Black101 6y agoit's why I often share screenshots of photos... to remove as much information from them as possible
- sloshnmosh 6y agoIs there a similar article online somewhere that can be read without having to enable JavaScript?
- eingaeKaiy8ujie 6y agoI can read it with JavaScript completely disabled.
- sorenjan 6y agoA lot of mobile cameras now take high resolution images (108 MP, 50 MP) and downsample them to something like 8 or 12 MP. Since this is done in the same way every time I guess any systematic noise could still be detected, but it will be attenuated and even more difficult to find, and that's before JPEG compression, multiple frames fused for HDR, and so on. Tying a specific camera to one or a few photos in a criminal case sounds extremely dubious. Natural images are full of different kinds of noise anyway, and each pixel only has 256 levels of intensity.
- elwell 6y agoIs it possible the two photos were exported from some photo software ten minutes after each other, and the export adjusts the EXIF timestamp? Probably less likely, but just positing another scenario.
- crazygringo 6y ago> Photo response non-uniformity, however, is far more difficult to extricate. I don't see why? Seems like all you need to do is take a photo of an evenly lit gray card, determine the variation of each pixel, and then apply the reverse of that to every photo you take. And a simple filter can even get around the "evenly lit" part trivially, as long as it's smoothly lit. (I.e. handle gradients.) The article doesn't mention this at all -- yet isn't this the kind of thing astronomy photographers do when stacking photos, to prevent the "fingerprint" from accumulating? Of course, it's not even clear this "fingerprint" is even remotely readable from average photos -- it seems like it would be completely indistinguishable in any scene with detailed textures. So it's really only in areas of blank walls, sky, etc. where it poses a risk.
- kortex 6y agoIt's difficult to extricate for the reasons you mentioned - various textures interfere with extracting it. But it's also surprisingly difficult to purge once you extract that fingerprint. Astronomers (I presume) do much more in the way of non-uniformity correction (NUC). Often one of the biggest differences between consumer cameras and industrial/scientific ones is the ability to continuously recalibrate them, either in firmware or in post. You could do the same with off-the-shelf cameras and some software, but there's little need most of the time.
- crazygringo 6y ago> But it's also surprisingly difficult to purge once you extract that fingerprint. Can you explain why? Is it not just a simple subtraction? E.g. is it not a pattern of predictably varying intensity per-pixel, but a spatial pattern of nondeterministic noise? So each individual pixel has a likelihood of contributing to the "fingerprint" in any given photo, but you don't know if it contributed in this one? Or does it totally predictable on the sensor, but the on-camera RAW processing followed by JPEG compression transform it in non-predictable ways, so that you'd need to extricate it on RAW data directly before any processing? Or is it something extremely non-linear that changes depending on pixel brightness per color channel, or is drastically different depending on exposure time? I'm super curious if you or anyone has actual knowledge here.
- amelius 6y ago> The photo timestamps, however, said otherwise. The images were taken 10 minutes apart. Perhaps I'm stupid but could it be possible that the camera clocks were not set correctly?
- cronix 6y agoAlso, what timestamp were they using for this comparison? EXIF data? Filename (some cameras store the filename of images/videos as the datetime it was taken)? Filesystem time it was written, and was that on the camera or when the files were dumped to a computer and saved there one after another sequentially? There could be several potential sources for this "timestamp," but I haven't seen the one they are talking about actually mentioned.
- SMAAART 6y agoELI5: if someone downloads photos that I have uploaded to a) Reddit b) Facebook c)Instagram can they access the Exif info? What if I have cropped and re-saved using GIMP or Mac's Preview?
- klyrs 6y agoGIMP has options to preserve or strip exif data in the Export tool. Can't speak with confidence about the other stuff that I don't use, but I expect that social media probably preserves it at least internally -- that should be really easy to test if you've got an account on the sites you're concerned about
- ymmyk 6y agoThen there are companies like Parler which didn’t even bother to remove the meta data. Unbelievably noob, they deserved to be shutdown even if I am generally pro free speech. Made it easy to find the white supremacists though.
- cronix 6y agoThe company didn't protect noob users from themselves?
- m463 6y agoWhen will manufacturers or others "test fire your camera" before it is sold and file the results? That database will be worth money to someone in the future (not the customer) I believe this is done for handguns - they test fire the gun, then record the way the firing pin marks a cartridge - all before it is sold.