Avoiding Camera Noise Signatures




About: Taking back the world, one hacked game console at a time ... Have you ever felt like the technology you love could be used against you? Or that the government is watching you .. a little too closely? Have...

If you take enough images with your digital camera, they can all be compared together and a unique signature can be determined. This means that even when you think that you are posting a photo anonymously to the internet, you are actually providing clues for the government to better tell who you are. The larger the sample size of images they have, the easier it is them to track down images coming from the same camera. Once they know all the images are coming from the same camera, all they then have to do is find that camera and take a picture to confirm it beyond a reasonable doubt.

It is important to remove this noise signature so that you cannot be tracked down. I cannot guarantee any of these methods will work beyond the shadow of a doubt because the woman doing research for the government on how to find the signature is very good. Check out her papers if you're really good at dense math, and pass along what you learn. I can only promise that this will make their work more difficult.

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Step 1: Remove the Camera Info

When you take an image with a digital camera, the camera itself leaves a data file which automatically identifies itself. This file is called an EXIF and usually has information like the make of the camera, the ISO setting, the date and time, the pixel setting, etc. This needs to be removed. The easiest way to remove this is to open photoshop and save it for web.

When you save, I recommend using a JPG compression with a quality setting of no better than 60%. This will add a lot of ugly noise make it slightly harder to create a noise signature.

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Step 2: Clean the Lens

Clean your camera's lens constantly with a non-scratch cloth that you can get for cleaning camera lenses or eye glasses. This will remove specks of dirt that will show up from image to image and never change. If there are pixels never changing on your camera then it makes it really easy to identify you. This is why it is important to crop the image.

Step 3: Crop and Resize the Image

If you have dirt on year lens, dead pixels or "hot" pixels, then it is really easy to find images from the same camera since they will all have static pixels. This means, from image to image there will always be a handful of pixels that don't change.

The way to get around this is by cropping and resizing the image. This will shift the position static pixels and when images are compared together make them just seem like noise.

This alone will not always remove the noise signature itself, but it is one way to make it harder to identify it.

Step 4: About the Noise Signature

So far I've only told you how to make it hard to tell a picture has come from your camera, but not how to remove the noise signature. The marks made by dirt on the lens and dead pixels is actually different than the noise signature that they use to keep track of what pictures you are taking.

The noise signature itself is actually due to thermal noise (environmental heat) and imperfections on the CCD itself. Professional photographers and astrophysicists have tried to compensate for this by creating cameras that evenly lights a CCD a moment before the image is taken to create a noise reference against the image being taken or by super-cooling the camera itself so that heat can't distort the CCD.

In your store-bought camera, it won't have either of these functions and so you will end up getting a lot of pseudo-random noise mainly on the last 3 bits of every pixel. This noise isn't really noticeable to the naked eye, but with a large enough image sample, they can create a noise profile and match almost with certain accuracy pictures from the same camera. Since the noise is dispersed throughout the image itself and tends to remain constant through certain standard image manipulations, it is hard to remove without destroying the image.

Step 5: Removing the Noise Signature

Ideally, you would remove the noise signature by making the image cleaner. It is noise after all. Although, determining which noise to remove isn't always clear.

It is probably more effective to remove the noise signature by creating more noise. One thing to try is to open Photoshop and save an image as a jpg using bicubic compression, resize it, crop it and then save it for web, again as a jpg (removing the exif) and finally save it for web again as a jpg using a quality of about 50. This should destroy the noise signature beyond recognition, but the image might not look too good.

It wouldn't be good to do this ever time either since you will end up creating a new "signature." The best thing to do is to save each image using a different elaborate method every time. For instance, you might convert something to a flash video, take a screenshot and then save for web as a jpg compressed with a quality of about 50.

It may not work, but you could also try adding a small amount of random noise to the red and green channels. This might actually clean up the image and remove the signature, but I'm not sure.

Step 6: Common Sense

If you're bothering to make your image anonymous, post it anonymously. Use a TOR server and if you have to register for an account to post it, create a new one for every couple of images. Make the images seem like they are coming from as many places as possible.

Step 7: Use a Film Camera

If you are really that concerned, use a film camera and scan your images using multiple scanners at multiple different corporate copy shops. The only downfall to this is that you actually have to go somewhere to scan the images and store employees or video cameras could maybe identify you. If you wait a few days before posting things online, it will make it harder for them to connect it with you.

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    78 Discussions

    From reading the .PDF file from your source there, she mentioned that image analysis has been performed on analog (film) cameras long before digital image analysis. Therefore, step 7 really won't give you a lot of options.


    9 years ago on Step 5

    This is going to be a bit technical, though can be written in a short python script using Python Imagimg Library:

    You can add random noise using some good pseudo-random generator, like Mersenne Twister (seed with something random) - choose random number of pixels at random positions and brighten/darken them a bit (or mess with both chroma and luma channels).

    Then use either nearest-neighbor or lanczos interpolation to resize image (instead of bicubic), they modify the frequency spectrum and histogram characteristics much more.

    The reason jpeg compression does the described degradation of noise is because jpeg quantization tables used for lower qualities used after discrete cosine transform basically remove highest frequencies ("the noise").


    9 years ago on Step 3

    I suggest either nearest neighbour or lanczos interpolation when scaling images. Lanczos is based on "ideal" sinc filter and can be configured as low-pass filter that removes noise (the statistical signature).

    For example, using lanczos interpolation when scaling image in GIMP, it screws up higher frequencies (the visible noise) quite considerably (measured with power spectral density and correlated to original image).

    See attached example measurement (shows PSD and correlation of frequencies spectrum after Fourier transform).

    1 reply

    9 years ago on Step 6

    If the government is going to go through this much work to prove you took a bunch of pictures, you're either a terrorist, a spy, or a kiddie pornographer.

    What this instructable lacks is a demonstration. A fairly simple one would be to take 4n pictures, where n is a big number, say 1,000 or 100,000, with the same camera in randomly different situations. Do not process the pictures. Create four composite images, summing the pixels of n pictures together (stacking them).

    Now process them. Subtract the mean value of each stack from that stack. Compute the standard deviation of all the pixels in a stack and divide the pixel values by the standard deviation.

    If the four processed stacks look similar, there is a strong signature in the image. If not, look for a more subtle signature. Calculate a spatial power spectrum from each processed stack. Similar power spectra MAY indicate a signature.

    Do a spatial correlation between each of the four stacked images. Similar correlations can also indicate a signature.

    If you find a "signature," reduce n by a factor of two and compare the 8 stacks. See how many images it takes to create a signature. Figure the government needs fewer pictures than you do, but probably not a lot fewer.

    How many of your pictures would they have to suspect to be from the same camera in order to get a signature?

    Just for kicks, do the same thing with a friend's camera of a different model and make. If it has a similar signature ...

    2 replies

    Reply 9 years ago on Introduction

    The "government" does not have to do anything on such a large scale as ElderBear says. (No insult intended to you ElderBear!)

    GOOGLE already has the processing power to do this kind of comparison; and they have the photographic database to test it with. Just as a phone number can be found in many cases via THE GOOGLE, photographs can be examined as well. It is all just data of one kind or another. Data is messy and leaves a trail of one kind or another for someone or something with a trained eye for it.

    w1n5t0n: Thank you for writing such a clear Instructable. Your style of presentation was very neat and well presented.


    Reply 9 years ago on Introduction

    "If the government is going to go through this much work to prove you took a bunch of pictures, you're either a terrorist, a spy, or a kiddie pornographer."

    Not everyone has the same faith in government that you do. Many don't find an appeal to safety argument to be a convincing one. I certainly don't.

    Tell me how being able to identify the noise pattern on a camera wouldn't also allow forged images? That is one potential abuse of this technology (which, given how useful it would be for law enforcement, and how trivial it would be to automate, will certainly end up being used in the courts). I don't think it is difficult to think of scenarios where this kind of identification could be problematic.

    In terms of the practical demonstration you mention, I would suggest that it would be better to take your sample images with the lens cap on (so only noise, and no real image data). Additionally, it would probably be wise to re-run the tests several times in a range of (operating) temperatures (given the effect on CCDs it has).

    As for the number of images required for identification, that number drops drastically with a CCD noise database at point of manufacture, or with deliberately modified CCDs (or camera firmware) - both techniques would be simple to implement and significantly reduce the samples required to identify.


    9 years ago on Step 4

    This isn't actually pseudo random noise. It is random noise that MAY be biased by process variation between elements of the CCD.


    9 years ago on Introduction

    There's nothing wrong with knowing how to do this. (As MahavishnuMan pointed out, information has no intent.) There's nothing wrong with the Instructable. I'm probably taking all this way too seriously. But the paranoia that often fuels this sort of thing can be more dangerous than the perceived threat.

    Let's say someone gets shot. The cops look at two guns, both of which match the bullet found in the corpse. Both owners claim innocence. The first gun is unaltered, with the owner's fingerprints where you'd expect them. The second is wiped clean of prints, and the serial number is filed off. Guess who's getting arrested.

    The same goes for computers. Say you've got a picture on your hard drive of this amazingly huge sparkler bomb your friend made for the fourth of july. Airport security sees fit to search your hard drive, and they find it. They ask you about it. You cooperate, answer their questions, and assure them that it was all on the level. I'm not saying they'll compliment your friend's bomb making skills and send you on your way, but the point is, they won't have sufficient grounds to suspect you of plotting an attack.

    If, however, the file is hidden, sanitized, distorted, and downloaded through a proxy server, and when asked about it you lie, or clam up and demand to see a lawyer, you've just earned yourself an FBI file and a body cavity search. That kind of forethought indicates that you were deliberately hiding something, and that's the sort of thing that law enforcement and airport security focus on. The more sophisticated your methods, the more interested they'll be (if, of course, your concealment efforts fail). Sure, they're wasting their time on you, but they wouldn't be doing their jobs if they didn't investigate someone who is clearly hiding something.

    I'm not saying that we shouldn't have some degree of privacy. I don't want to take the airport security guys on a guided tour of my hard drive any more than I want to install a breathalyzer ignition lockout in my car, or put a tracking chip in my arm. My point is that in all but the most exceptional circumstances, this kind of tampering is more trouble than it's worth. Unless we have something to hide, being paranoid only makes others paranoid about us. We cannot live in fear of one another.

    Personally, I make a point to not put anything online that I wouldn't put my name on. If "they" (the fearful entity I've heard so much about) do in fact come for me, well, I'll deal with it. Better to die on your feet than live on your knees, right?


    9 years ago on Introduction

    Bit narrow minded of some members who seem to think that the US is the beginning and end of the entire world when it comes to things like rights and that any system different to yours must be somehow flawed.

    It isn't.

    I think that the "Right of free speech' needs to be put into context here . You may have a right to free speech in the USA but in Australia and most of the rest of the western world you do not have this 'right'. You instead are not stopped from voicing your opinion as there is no legal means of stopping you from voicing your opnion. There is a difference.

    We have compulsory electrol registration and voting for all citizens aged 18 and over who are not in jail for longer than 6 months or classified as mentaly incompetent to vote etc.  It is also legal to drink alcohol, get married, own property, sign contracts, be called for jury duty at 18 etc as well.

    3 replies

    Reply 9 years ago on Introduction

    I have to disagree with you. All the democratic countries have the right of free speech some way or another included in their constitution, just like the US. In many times it simple has to be included in the constitution or every time a new government would come they could change the law with plain majority and start jailing people for their opinions. Having it declared in the constitution makes it a tad harder....


    Reply 9 years ago on Introduction

    Unfortunately Australia has no constitution. To the best of my knowledge nobody has been sent to gaol so far for voicing an opinion in Australia, but freedom of speech is not a right held by Australian citizens and there is no actual law about it. Suing for defamation works somewhat better in Australia that it does in the US.

    Yes, I agree that this is a problem and things could become a lot worse, but that's the way it is right now.


    Reply 9 years ago on Introduction

    http://australianpolitics.com/articles/constitution/full-text-of-the-australian-constitution-as-amended A full copy of Australia's non existent constitution can be found by clicking on the link above Plexy.

    http://www.aph.gov.au/LIBRARY/pubs/rn/2001-02/02rn42.htm Section of the non existant constitution pertaining to freedom of speach.

    Freedom of Speech and the Constitution
    The Australian Constitution does not have any express provision relating to freedom of speech. In theory, therefore, the Commonwealth Parliament may restrict or censor speech through censorship legislation or other laws, as long as they are otherwise within constitutional power. The Constitution consists mainly of provisions relating to the structure of the Commonwealth Parliament, executive government and the federal judicial system.(6) There is no list of personal rights or freedoms which may be enforced in the courts. There are however some provisions relating to personal rights such as the right to trial by jury (section 80), and the right to freedom of religion (section 116).


    I couldn't help but weigh in after reading the responses to this interesting (and informative) Instructable.

    Over the past decade, the attitudes of both government and citizen have changed considerably with regards to how comfortable we are with perceived threats, as well as how comfortable we can become with opening our lives to outside inspection in an attempt to counter these threats.  Of course, we all know what got the ball rolling and when, and I can't think of a single person in the world that wasn't rocked to their core.  When our hearts sank into piles of smoldering debris, we were all forced to reevaluate how safe we thought we were, and what we would be willing to do to recover the tattered shred of naive security we wore every day.

    Fear is instinct - it is a reaction that sharpens our wits and keep us alive as it had for millennia.  But, fear can dull our senses with a single hammer-blow, sending us careening into a wild stampede through the clearest path of escape, leading us eventually over a cliff to our demise with the rest of the herd.

    We were instructed as children that we were born free, and had inalienable rights with laws and government to protect them.  After this event, we failed to ask ourselves how the changes taking place in our laws and government stand in direct conflict with the core values we had been taught.  We saw these measures as a means to bring swift justice to the guilty, an instrument that would wrest the cloak of liberty from parties we felt deserved no liberty.

    What we didn't realize then, and few realize today, is that the same legal vehicle introduced to stamp out terrorist acts also allow the government the reach to monitor everyone indiscriminately; regardless of whether anyone agrees that their government chooses to act on this ability, the potential exists nonetheless.

    And, as any history scholar can tell you, governmental power so absolute corrupts absolutely.

    For any readers who view this as scaremongering, remember the fevered pitch under which you chanted "I have nothing to hide" just nine years ago.

    Technology's reach and influence in our daily lives has rapidly increased since then.  Furthermore, we have embraced the ubiquity of it as a positive change - a way to broaden our horizons and shrink our borders.  We share pictures on Flickr, then Twitter about them, and get on Facebook to tell all our friends about it.  We freely offer this information to anyone with an internet connection, and if a suspicious party with the authority takes interest in us, they can use this information we volunteer for their own interests.  This may seem Orwellian, but it's not - we, in this sense, are our own Big Brother.

    It is no secret that this information exists, nor is it a secret that the government, utilities, insurance companies, and even your employer use this information on a daily basis for thousands of reasons.  When we hear someone warning us of these reasons that sound like science fiction and are far removed from the intended use of the information, we scoff and dismiss it as paranoia.

    We often forget that information itself has no intent.  It's no secret that, while Social Security numbers were never intended to be used as personally identifiable, you can't live in the US beyond a cardboard box without one.  But now if you post a happy picture of you smiling on vacation, you could lose your insurance.  If you have a state-issued photo ID, your face is currently being matched against known criminals and suspects.  The only question now remains, what constitutes a crime anymore - and could you be a suspect?

    After that horrific day, a new act was hurriedly signed; not even those who signed it read it or understood its contents.  If such an act, one that usurps the very rights granted to all citizens in the interest of protecting the innocent, can slip under the radar, then you must ask yourself what else can be signed into law.

    As of 2001, the means exist to hold you indefinitely without a lawyer for questioning over charges which do not have to be made clear to you or anyone else.  Under this same act, all criminals (no matter how small the crime) are a potential threat and are within the scope of suspicion.  All anyone needs is a reason to do so, and some sort of evidence to put you in the wrong place at the wrong time.

    But don't worry - you have nothing to hide.


    9 years ago on Introduction

    I find it funny, tracing people's movements through images posted online would be going a bit too far, unless it was for dealing with criminal acts, cos the average person, such as myself, couldn't care less if I'm being profiled by some secretive government body, some creepy organisation or an online stalker, but that said, I always crop my images, cos my camera isn't that great... :P

    Still, it's a very interesting read about what cameras do with the information and how they store it, might explain why my photos are about 2MB for a single 1280x1024 JPEG picture... :S


    11 years ago on Introduction

    It may not happen where you live, but there are places in the world where the government gets very uptight about images of some of their activities becoming public. Not everyone seeking anonymity is paranoid.

    4 replies

    Reply 11 years ago on Introduction

    darus67 is dead spot on. The argument of "If you aren't doing anything wrong, you'd have nothing to hide" is insidious and shameful. We all, as human beings, have a right to privacy and free speech - but, in a world where one's every move is recorded, tracked, collated, quantified, and reported (and we've seen proof positive that it is, at least in places like London - I' m sure many other parts of the world are the same), then the only way to exercise these rights is through so-called paranoia. As they quote so often on the Internet these days, "If you give me six lines written by the most honest man, I will find something in them to hang him." Thanks, darus67!

    Dream Dragongmoon

    Reply 11 years ago on Introduction

    What's "Shameful and insidious" is that some people insist on ABUSING the right to privacy. Your so called right to privacy is GONE, it was stolen in little pieces by every criminal or terrorist you've ever heard of, and a lot you haven't. It's sad, but it's a fact. Accept it, live with it, or take it up with the people who use YOUR "rights" to conceal their own shameful and insidious agendas. For my two penny worth, anything that identifies an image as MY property is a good thing. Anything that helps identify a criminal or prove the innocence of a law abiding citizen should be encouraged, and anyone who is researching additional ways to fight that particular battle is a hero. I did find this Instructable very interesting however and I'm grateful to the original poster for bringing it to my attention.

    gmoonDream Dragon

    Reply 11 years ago on Introduction

    and anyone who is researching additional ways to fight that particular battle is a hero.

    I really think that's the point of this instructable--that the "battle" has far overshot it's legitimate anti-terrorism origins.

    Accept it, live with it, or take it up with the people who use YOUR "rights" to conceal their own shameful and insidious agendas.

    Hey, I don't have to accept anything of the sort. FAR more people have died in previous wars specifically to protect my rights, and I'm not about to concede them without a ruckus. And that is what's happening here--people fighting shameful and insidious agendas.