Digital Photos Give Away a Camera's Make and Model 260
holy_calamity writes "Engineers at Polytechnic University Brooklyn have discovered that digital snaps shorn of any metadata still reveal the make and model of camera used to take them. It is possible to work backwards from the relationships of neighboring pixel values in a shot to identify the model-specific demosaicing algorithm that combines red, green, and blue pixels on the sensor into color image pixels. Forensics teams are already licking their chops."
Raw images? (Score:5, Insightful)
So, if I shoot in raw mode, and then postprocess in software to get a jpeg, the demosaicing signature should merely identify the software, right?
Of course, I wouldn't be surprised to learn that the distortion uniquely identifies the lens used...
So What? (Score:5, Insightful)
So what if they can identify the make and model of camera. I own a D70. There are 300 billion d70 out there. Good luck on tracking a picture to my camera.
For what purpose? (Score:2, Insightful)
I can only see this, in a positive light, as uncovering fraud or deception -possibly even supporting a claim as to the veracity of a witnesses' testimony to photographing a crime- instead of this being used in a nefarious way. Although, once the algorithm is well understood, certain 'non-well-intentioned' organizations or individuals will use this for evil instead of good. But in the meantime, how would this worry the average digital shutterbug?
Re:Really... (Score:5, Insightful)
Oh my! (Score:5, Insightful)
I better sell my Nikon D300. They'll be able to trace it back to me. Or one of the other gazillion people who also bought one. Hmm... on second thought...
Re:So What? (Score:5, Insightful)
> Good luck on tracking a picture to my camera.
That's not the purpose. Knowing the photo was taken with a D70 eliminates all the zillions of cameras out there that aren't D70s. It's like knowing that a bank robber is a 6' tall blue-eyed blond male.
Re:So What? (Score:2, Insightful)
So what if they can identify the make and model of camera. I own a D70. There are 300 billion d70 out there. Good luck on tracking a picture to my camera.
RTFA:
While many people own the same camera models, Pollitt believes that this technique can still be used forensically. He says that because digital cameras have a shelf life of only 18 months, this can help to narrow down when and where it was sold.
Just because it won't immediately narrow it down to a single suspect with perfect accuracy doesn't mean it won't be helpful in investigations.
Re:stretch? (Score:5, Insightful)
Re:Meta data? (Score:5, Insightful)
> Of course someone who is stripping the exif data will never resize the image and run
> some sharpening over the image just to cover their traces, right?
Some will, some won't. Criminals are notoriously careless and stupid.
> Yep, this one was taken by a Canon Powershot A510 of which only 5.7 million were sold.
> We also know that this particular model was either sold in North America, Japan, Europe,
> Africa, Australia, South East Asia and South America. That should narrow it down.
Yes. Of the 18 initial suspects only two own that camera. Concentrate your investigation on them.
Re:So What? (Score:5, Insightful)
Forensically, it's as useful as saying "this bullet came out of this model pistol." Not conclusive by itself, but one piece of a larger puzzle.
99% of criminal investigation is eliminating who didn't do it, and this can be useful for that.
Re:Killjoy (Score:4, Insightful)
That isn't the conclusion that the author came to. If you compare http://www.luminous-landscape.com/images-85/h2.jpg [luminous-landscape.com] and http://www.luminous-landscape.com/images-85/g10-comp.jpg [luminous-landscape.com] there is definitely a different between the yellows and the depth of focus on the expensive camera is far better (compare the red leaves on the upper left).
Depth of field isn't a question of better or worse, you know, it's just different. If you want to poke at that story, you might just point out that a the limited image size makes the comparison pointless. These days, cheap digital cameras make incredibly expensive pro cameras more useful for either flexibility or niche markets (like >13" prints). That doesn't mean professional cameras aren't worth it, just that they're not worth it for everything.
Re:stretch? (Score:2, Insightful)
That whooshing sound you hear is the joke flying over your head.
This just in... (Score:4, Insightful)
Cops didn't realize that most pictures posted on the interweb thing are usually post processed.
Re:So What? (Score:5, Insightful)
So what if they can identify the make and model of camera. I own a D70. There are 300 billion d70 out there. Good luck on tracking a picture to my camera.
Its useful the same way knowing the car that raced away from the scene of the crime used a particular tire, with a particular wheelbase. Or that a bullet was fired from a particular make of gun.
Neither will positively identify anyone, but if you were already a 'person of interest' in a long list of people peripherally related to a case that detail might put you on a MUCH shorter list if it comes up that you have that model. Plus its useful when they are asking a judge for a warrant. Judges really like specificity with warrants... A "We want to search his home and car for a Canon Powershot X"; he blogged here about buying a Canon Powershot X, he was caught on this surveillance tape leaving the scene carrying an indistinct object, the dimensions and shape of which are consistent with a Powershot X, and we know the photos in question were taken with a Canon Powershot X"... that's got a lot more weight than... "We want to search this guy for a digital camera, because a witness said he owns a camera, and he was caught on tape holding an indistinct smallish object which could be a camera, oh... and the photos we're interested were taken with a camera."
A reasonable person would view the second as a complete fishing expedition, based on no evidence, practically everyone has a camera and he could have been holding anything on that tape. The first request is specific - the photos of interest were taken with that model, and there is reason to beleive the person HAS that particular model, and that he had it with him on the that tape. Sure it could be a coincidence, but a warrant for that particular camera if he has one to check it out, might not be unreasonable.
Its also not unlikely that they can pair photos to a particular camera if they have both on hand due to micro-scrathes and other unique lens defects... the same way they can pair laser pritners to printed output.
Re:So What? (Score:1, Insightful)
99% of criminal investigation is eliminating who didn't do it
Unfortunately 99% of prosecution is sweeping those bits under the rug so the prosecutor can pretend to be tough on crime and leech ever more from society at higher and higher positions.
Re:stretch? (Score:4, Insightful)
or you could just use a camera with a Foveon X3 sensor [wikipedia.org]. there's no demosaicing involved since it employs 3 vertically stacked photodiodes (red, green, blue) at each pixel sensor to capture color information.
here [wikipedia.org] is a diagram showing how a multijunction photosensor works. unlike bayer filter sensors, Foveon X3 sensors produce no color artifacts.
Re:stretch? (Score:4, Insightful)
Re:Oh my! (Score:3, Insightful)
I know what you mean! The thought of the government being able to tell what digital camera I used to take a picture of myself for my facebook profile is terrifying.
This has abuse potential (Score:2, Insightful)
This sounds like the equivalent of "registering" typewriters with the government in nations once behind the Iron Curtain. It is no different than obtaining ballistic signatures from firearms at the manufacturer level. Yet one more reason to distrust governments.
Re:So What? (Score:2, Insightful)
It's clearly a technique for child porn investigations. If you have a suspect who owns the same kind of camera you determined was used to take the photo in question, which the investigators most certainly didn't get from the photographer them self, you can know whether to search for more evidence or to eliminate them from your suspect list.
Most people who do this kind of thing are not necessarily going to realize this is possible, so aren't going to think of the obvious solution, which is to borrow someone else's camera or to own two cameras (one bought with cash) and hide the one used for dirty deeds really, really well (in a train station locker, say.)
So basically this is pretty weak evidence, and not that great of an investigative tool, in my opinion. Of course, zealous investigators are going to push stuff like this as fool-proof evidence, despite the multiple problems with this such as I just described in the previous paragraph.
Re:Killjoy (Score:4, Insightful)
Looking at the images at 100% scale and you can see a tremendous difference in the amount of noise in the backgrounds. That is mostly caused by the smaller size of the CCDs and the quality of the sensor itself. Plus, the higher end cameras have far better noise reduction software built in.
In addition to noise, the small digitals show lots of other image degradation as compared to a dSLR. They lack sharpness and have issues with distortion, color accuracy and chromatic aberration. The ultimate source of all of those issues is the glass. You simply can't get the same level of quality out of a half-inch lens as out of series of two-inch lenses (assuming similar technology applied to both).
I just shake my head at the ever-increasing megapixel numbers on compact digital cameras. I know they're great for marketing, but for the camera owners they do nothing but produce bigger files, with no better image quality than if they'd had a smaller pixel count. Once you get beyond the resolution of the glass, there's just no point in adding more pixels.
I just read the Haselblad/Canon comparison, though, and I have to point out that the Canon G10 is not what most people think of when you say "cheap digital". It's not an SLR, but it's close, with larger, better glass than most P&S cameras and a larger sensor. 15MP is a bit much for those lenses and that sensor size, but it's not that crazy.
Rethink (Score:3, Insightful)
At first blush this struck me as similar to the printers that revealed a specific device by a faint set of dots printed on each piece of paper. On further thought, it occurs to me that the difference would be that the dot-tracking was shady where-as this is a triumph of statistical observation. The former being slimy and the latter sheer brilliance.
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http://techdojo.org/ [techdojo.org]
Re:So What? (Score:2, Insightful)
With child porn investigations this probably counts as sufficient evidence to convict someone seeing how quickly people go rabid when the subject comes up.
Re:stretch? (Score:4, Insightful)
Add to that the fact that reducing the image size will probably get rid of the evidence, using a raw image and demosaicing on a PC will tell you what software was used instead of what camera was used, there are a lot of limitations.
On the other hand, most people do not know all this - then again, most people are unlikely to think of deleting the meta-data either.
Re:Oh my! (Score:5, Insightful)
I better sell my Nikon D300. They'll be able to trace it back to me. Or one of the other gazillion people who also bought one. Hmm... on second thought...
you're missing the point. there usually are other factors in play in any investigation. having only the camera make to go by is useless, but not so if you've managed to narrow - through other criteria - your suspect list down to 10.
Re:stretch? (Score:3, Insightful)
Re:stretch? (Score:3, Insightful)
It does, but rather than narrowing it down to a particular model, it narrows it down to any digital SLR (and maybe other types) camera made by Sigma.
Given how few Sigma cameras are sold compared to any popular model by the big manufacturers, that isn't say much, right? At the moment, anyway.
Re:stretch? (Score:2, Insightful)
If you have the computer the image was stored on, you already have more information than what this article deals with. There is no point finding out what camera made the image if you can check for finger prints/DNA on the computer itself. And that is not even getting into searching all the files on the PC and tracing all activity. Also, how did the person in question get to that computer? Is the owner of the PC related, etc.
Re:Oh my! (Score:4, Insightful)
Or you could shoot RAW and then the camera doesn't do any demosaicing at all.
shoot raw (Score:3, Insightful)
HOLY SHIT!!!! (Score:3, Insightful)
They figured out how to read the EXIM data stream.
BRILLIANT!
Re:So What? (Score:3, Insightful)
It's clearly a technique for child porn investigations.
Maybe I'm naive, but it took this long into the discussion thread for somebody to explain why this is even a story. I hadn't thought of that (because I'm a decent human) and I guess everyone else *thought* it, but were a bit uncomfortable stating what is otherwise totally obvious to most folks.
Re:the downside (Score:2, Insightful)
yes it was. Now tell me why the police know what model camera you own to begin with without a search warrant and we're all set.