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Digital Photos Give Away a Camera's Make and Model
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."
As even the cellphones are producing 3 megapixel images now, very few people need to be passing full-resolution originals around. If you scale the image down to a screen-usable 1 megapixel image, there's not going to be a lot of bayer mosaicking information still available.
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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...
After the sensor takes the RAW data, the camera processes the image (some noise reduction, curves, and compression) to get a jpg. Since this conversion would vary between manufacturers (or even RAW software) I'd imagine that the process would leave behind similar "fingerprints."
They don't have to. All they have to do is say they used forensics just like on CSI, and it shows it was taken by the same kind of camera you own. Sure, you can say there are a lot of them out there so it proves nothing. But you know who else says that? The bad guys on CSI, and their smug, latte drinking lawyers. Always demanding warrants and to be released if they aren't being charged with anything! EVIL
ASCII stupid question, get a stupid ANSI
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...
"I'd rather be a lightning rod than a seismometer." -Ken Kesey
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:
The bad guys on CSI, and their smug, latte drinking lawyers. Always demanding warrants and to be released if they aren't being charged with anything! EVIL
The only EVIL on CSI shows is the way the motherfucking cops use extortion.
"You don't want to give up privileged information on this guy? Fine, we'll be back with a warrant. Of course, we may have to dismantle your office for a couple of weeks to do a thorough search. What does a couple of weeks mean to your business? You do understand, don't you, that when we seize (God, how those bastards love the word "seize") your computer, our clumsy techs might return it with some important files no longer readable? So sorry. ... Oh, yes, ma'am, that's the perp we were inquiring about. Thank you for your cooperation."
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.
Yes... CSI is very realistic in that regard.
Standard police tactic in real life, i'm sure.
Use fear/insinuation to get whatever info needed.
Except IRL it's not merely extortion, insinuated threats like that are all real.
There are photodesk editors with experience who claim to be able to identify the camera model, the lens used and the post processing software used to produce the jpeg / tif file. This is possible due to various characteristics that are introduced at each stage in the digital photographic process. Giveaways for the camera body used are the base resolution, any colour casts in the image, iso performance, dynamic range. For instance many Canon DSLRs are criticised for producing muddy greens in their images - especially at higher ISOs as the dynamic range is pushed to extremes. Then you can usually work out the lens - by the obvious field of view first, then the flaws in the shot - various lenses from various manufacturers have different flaws. For instance the 70-200 f/2.8 from Nikon has characteristic vignetting that can often be noticed even after post processing, then other cheaper lenses give various defects to the image such as chromatic aberation. The flaws in the image give away the body and lens. Also the sensor used gives certain image characteristics that are fairly easy to spot even to the keen amateur photogs eye - for instance telling the difference between a full frame sensor and a smaller APS sized sensor - the full frame image typically has a much smoother more film like attributes with less digital artifacts. Also the same can be said for post processing. This software usually leaves various characteristics - that remain with the image, and this varies for each different software vendor.
So this is all possible to a well trained human eye - don't see why it shouldn't be possible in software - but not sure of the real benefits of being able to identify this - as many photogs often leave the exif data - and that tells you everything.