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Interpol Unscrambles Doctored Photo In Manhunt
Posted by
kdawson
on Tue Oct 09, 2007 05:39 AM
from the blur-schmlur dept.
from the blur-schmlur dept.
jackpot777 writes in with an AP story out of Paris reporting that Interpol has distributed photos of a man suspected of sexually exploiting children. The images were recovered from pictures taken off the Internet in which the man's face had been blurred using something like Photoshop's Filter > Distort > Twirl tool. German police were able to recover recognizable images of the man, whose identity and nationality are not known. Interpol would not discuss the techniques used to recover the images. jackpot777 writes: "It does show one interesting facet of internet privacy that has also been noted with topics ranging from reading blurred check numbers in images to Google's plan to blur out license plate and face data for Street View. And that is: blurring is not the same as completely obscuring. As computers become more adept at extrapolating data of different types, your identity isn't safe unless you completely cover all those identifying features."
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Pictures (Score:5, Informative)
Re:Pictures (Score:5, Informative)
The spiral distort effect is simply a mathematical function to map one point in a rectangular mesh to another. You basically convert integer pixel coordinates into a floating-point coordinate system with the origin at the centre, apply a rotation based on the distance from the origin, convert back into integer pixel coordinates and transfer the pixel data.
Consequently, since every pixel is remapped to a new position, the transformation can be reversed.
Parent
Way easier than that.... (Score:5, Funny)
Parent
Re:Crucial overlooked ideas (Score:5, Insightful)
It probably helps a LOT that in several of the images, there's a strong line visible in the background. Measure the twirl of that, you've got your benchmark right there. Center of the twirl is probably easy enough to locate too. So there's your twist, and where to apply it.
It's a good thing so many criminals are dumb. It's the smart ones that you have to worry more about.
Parent
Re:Crucial overlooked ideas (Score:5, Funny)
Who says he's dumb? If he carefully photoshopped someone else's face onto his, and then applied the easy-to-remove swirl, he now has the entire planet searching for the wrong guy....
Parent
Amazing technology (Score:5, Funny)
Re:Amazing technology (Score:5, Funny)
Parent
Interpol not the ones to descramble (Score:5, Informative)
These pictures have been produced by specialists from Germany's federal police force, the Bundeskriminalamt, working from originals found on the Internet, which had been digitally altered to disguise the man's face.
Re:Interpol not the ones to descramble (Score:5, Funny)
Parent
The actual AP article (Score:5, Informative)
Super-sekr1t unblurring techniques (Score:5, Insightful)
Re:Super-sekr1t unblurring techniques (Score:5, Interesting)
Wild ass guess ahead...
Interpol geeks probably ran some tests to determine approximately how much twirl was applied to the original image and then created a 24bit image slightly larger than the twirled area assigning a unique 24 bit value to each pixel and then applied the same amount of twirl.
They could then look at the twirled test image and come up with a mapping of twirled pixels to untwirled pixels. This information could be used to "untwirl" the original image by grabbing the pixels at the twirled coordinates and moving them back to where the mapping says they probably originated.
Of course there would be some pixels lost and extra pixels created during the original twirling but chances are the original image could be approximated fairly well by interpolating between the recovered pixels. You'd not get a picture perfect result but something somewhat blurry as can be seen in the recovered pixels.
Of course they might have done something more mathematical but if I was going to try this myself I'd probably just give the method I described above a shot first and see if I came up with something looking like a face.
Parent
Re:Super-sekr1t unblurring techniques (Score:5, Interesting)
William
Parent
Re:Super-sekr1t unblurring techniques (Score:5, Interesting)
With more time and higher quality images, I'm sure it wouldn't be any trouble at all, it just needed the initial insight to use the "swirl in opposite direction" idea.
Parent
Re:Super-sekr1t unblurring techniques (Score:5, Informative)
Then I did a -999 deg twirl, and it totally undid it - almost perfectly.
I'm surprised it worked so well actually, I was assuming that it would still be more distortored since I thought the result would be more of a hash, but the algorithm used looks to be 99% reversable - at least in the case of photoshops' distort/twirl effect.
Parent
Re:Super-sekr1t unblurring techniques (Score:5, Funny)
Parent
Blurring different from twirling... (Score:5, Informative)
A blur on the other hand, especially a gaussian blur, will mix pixels together in such a way that any recovered image will be one of many possible outcomes.
Then again, removing information, by pixellating for example, would be best.
Re:Blurring different from twirling... (Score:5, Funny)
Parent
Re:Blurring different from twirling... (Score:5, Insightful)
The link about cheques in the summary tells more (if it's that old article I think it is).
Parent
Re:Blurring different from twirling... (Score:5, Funny)
Parent
Hardly Rocket Science (Score:5, Insightful)
I showed this to my PS using friend and he shurgged, said 'Just do a radial blur in the opposite direction' and 30 seconds later had a picture about 80-90% as good as the one they're waving about as being the result of some super secret methodology.
It does strike me as a bit stupid explaining it all - now crims will just use better techniques for blurring themselves out. The media, law enforcement agencies are doing this more and more and it's insane - "we just had an idea for a terrorist attack that might happen and here it is in full", "This is foresnic evidence that allowed us to catch the crim" and so on.
Re:Hardly Rocket Science (Score:5, Insightful)
It does strike me as a bit stupid explaining it all - now crims will just use better techniques for blurring themselves out. The media, law enforcement agencies are doing this more and more and it's insane - "we just had an idea for a terrorist attack that might happen and here it is in full", "This is foresnic evidence that allowed us to catch the crim" and so on.
Yup, they spun it (pun intended) into cheap PR. The problem is, it's not that they are super smart, it's that the criminal was super stupid.
And it'll make anyone with basic image processing skills question their overall expertise if they'd brag about untwirl.
That said, the average folk will definitely be impressed. I knew a guy who inverted his photo in attempt to protect his identity (no, he didn't molest children). Imagine his shock when I took the inverted photo, inverted it again arriving at the original.
To him I'm probably some sorta super genius who used sophisticated data restoration hack. To a guy with basic knowledge, it's nothing worth noting.
To see how blur can restore detail not visible to the naked eye, check out Focus Magic [focusmagic.com]. Not as easy as untwirl, but gives you an idea. This is because the blur distribution (usually gaussian if digital, or linear with cameras) gives away the possible origin position of the pixels.
If you pixelize however, with big enough square, you lose real resolution and that's much harder to restore anything interesting out of (it's not like in movies, with the unlimited extrapolation techniques, as we all know).
Other gotchas: covering with black rectangle but leaving it only 1-2% transparent. Looks solid, but data can be recovered.
And a very common other method: people keep leaving their name and camera model in the meta info of the image. Easy to check out via right-click>Properties in Windows.
PS: it was "twirl", not "radial blur" btw.
Parent
In other news... (Score:5, Funny)
New laws were passed today, making it a felony to obscure, obfuscate, scramble, cover or otherwise purposely mask your identity by modifying a digital image for the purpose of avoiding identification by law enforcement agencies.
Hmm (Score:5, Funny)
More Headlines Like This, Please (Score:5, Funny)
"Interpol Unscrambles Doctored Photo In Manhunt"
"Interpol Unlocks Les Paul in Guitar Hero II"
"Interpol Tracks Down Level -1 in Super Mario Bros."
"Interpol Acquires 'Marathon Man' Achievement in Halo III"
"Interpol Microwaves Weird Ed's Hamster in Maniac Mansion"