Untwirling photo of a suspected pedophile
D Brown says: "NY Times blog piece about Interpol's 'untwirling' of a photoshop-twirled photo, in the pursuit of a pedophile. Didn't know you could untwirl! Apparently the criminals didn't either, and Interpol's not telling how."
Link UPDATE: The Interpol's fantabulous untwirling secret is a built-in Photoshop feature, according to BB commenter DHL: "The technique is very simple. In Photoshop, make a round marquee centered on the centerpoint of the twirled image, then full negative setting on the twirl filter. I was able to download a larger image from the Interpol site and it worked perfectly."About 200 photos of the suspect with 12 different young boys were located on the Internet in December 2004, an Interpol official said. But in each image, his face was obscured, apparently by use of a standard Adobe Photoshop effect called twirl, which is used by digital artists to manipulate images.
Apparently, the suspect, or whoever handled the pictures, did not think it was possible to reverse the twirling, a capability that at least one Interpol official was intent on keeping confidential.
the latest
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"a capability that at least one Interpol official was intent on keeping confidential."
cause its a huuuuuge secret.
So... wouldn't the confidential method simply to use Photoshop to twirl in the opposite direction?
Yet another great example of a photoshop nerd saving the world from evil!
Presumably, the 'top secret' method would be setting Photoshop's twirl tool to a negative number.
(though it wouldn't work with the small/compressed version provided here)
Twirling in the opposite direction, eh? Crack team of Photoshop experts these interpol officials are.
Ask Interpol if they have any "thumb-removal" plugins for me, eh?
Actually there are several different ways of un-twirling. While Photoshops' "negative value" twirl will give some result, Matlab can be used to un-twirl and in some cases even un-blur images that have been otherwise manipulated. There are several documented algorithms that can be used to distort and un-distort images.
The problem is pixels. Reverse-gaussian transforms can be applied and such, but if the pixel data is destroyed, you can't just recover it. Only interpolate what's still there.
Nobody's said it, so I have to: that dude has one hell of a child molester stare going on.
@ TGG161
Yep, the technique is very simple. In Photoshop, make a round marquee centered on the centerpoint of the twirled image, then full negative setting on the twirl filter.
I was able to download a larger image from the Interpol site and it worked perfectly.
As TGG161 said, you just use a negative number. The trick is finding the proper number, but that's just trial and error. This is no problem. I've replicated it, in fact.
Why the hell would Interpol keep the details a 'secret' anyhow? Are they afraid molesters' images will be untwirled by someone else? Do they think that molesters will keep doing this now that it can be reversed, if they don't know HOW it's being reversed? WTF?
Checking now... Yes. This is possible. Simply run the filter back with negative values and it comes right back.
This is also possible in The Gimp, a freely avialable tool that you can download and use without paying a dime for Photochop.
"Checking now... Yes. This is possible. Simply run the filter back with negative values and it comes right back."
yep. i learned this playing around with my first photo editing program in the 90's when just playing with twirl filters was almost as fun as a video game.
This is the technological equivalent of putting a jpg in a zip file and renaming the extension, and then classifying the reversal process.
I'm reminded of a police release I read about growing opium poppies, saying they were so difficult to cultivate that it would be impossible for most phds to do so if they tried. Of course, poppies are largely self-seeding, and most of the world's supply is grown by millions of illiterate farmers throughout Asia.
"Do they think that molesters will keep doing this now that it can be reversed, if they don't know HOW it's being reversed? WTF"
Criminals are dumb plain and simple. A lot of them still believe the old urban legend that an undercover police officer has to stop being undercover if asked "are you a cop?".
Molesters often form networks comprised of guess what molesters who share tips on how to avoid police, where to go to snatch kids who won't talk, how to avoid having their images of child porn not be found on the computers they take in to be repaired. So if a false method of avoiding police becomes standard among these molesters then they will for example post phots of themselves abusing children on the web in very public areas that will certainty be found out about by the police. The police will then easily reverse the image allowing them to identify and thereby more easily track down the molester. Since the molesters wouldn't know that was how they were found out they would continue to use the technique thinking they wouldn't be caught.
Though it's not a huge secret how to untwirl a photo like this...there are valid reasons for not shouting from the moutaintops how they did it. Here's a snippet from the news story about this:
"Tipping criminals off to the techniques that police have at their disposal could also prompt them to better hide their identities."
you mean like simply cutting the face out entirely?
face it, this was a freebie, if it happens again it will be because a criminal didn't see this story at ALL, not because he didn't know about their de-swirling techniques.
It's like a laminar flow effect :)
http://www.youtube.com/watch?v=p08_KlTKP50
seriously, some info can be retrieved from
non updated thumbnails and EXIF data, after
editing, and some warp effects are reversible,
even the "randomness" is sometimes calculable.
Nothing like and old and trusty solid black block
of privacy, and a program like jpgclean to
remove any embedded metadata.
Fred the Anonymous
A slightly more sophisticated technique is used in the pixelization of genitalia on some Japanese porn, primarily online hentai manga.
Blocks of the image have mosaics pixelization applied with a password, the same password can later be used to reverse the mosaic.
it is a huuuuuge secret, the lore of the otaku.
Twirling/untwirling is some stupid pixel trick I remember seeing at least a decade ago on some how to site, maybe even one of those Adobe tutorials.
This twirling as concealment is in fact just a graphical equivalent of very bad crypto. The plaintext is the original image. This is just a series of numbers. The guy then applied a widely known mathematical algorithm to that a set of numbers to obtain the "concealtext". Problem is that anyone that knows the algorithm can obtain the original image (or a close enough one given that there are some variables) without much ado.
Techniques such as twirling or blurring or pixelating are not foolproof methods of visual obfuscation. If you want to hide information, you should obscure it completely.
This story appeared last night on 60 Minutes. See "The Man from Interpol" at
http://www.cbsnews.com/sections/60minutes/main3415.shtml
"#17 posted by Cpt. Tim , October 8, 2007 2:26 PM:
you mean like simply cutting the face out entirely?
face it, this was a freebie, if it happens again it will be because a criminal didn't see this story at ALL, not because he didn't know about their de-swirling techniques."
Oh no, I totally agree with you. If he actually thought that being swirled would protect him from getting caught, he's an idiot. Well, clearly he's an idiot to begin with.
I think that the cops are just hoping that other pedophiles will be just as stupid, and they're worried that by pointing out how dumb this is, they'll do something "smarter" to obscure their identities. But honestly, if they're this stupid to begin with, how genius could any of their new ideas be?
Forget Photoshop - I'd like to tattoo a permanent red bullseye on this creep's forehead.
This weirdo must want to get caught. You can't underestimate anything in today's world, especially after it was announced that the first synthetic chromosome has been successfully created.
"Forget Photoshop - I'd like to tattoo a permanent red bullseye on this creep's forehead."
Oh no! India's full of child molesters!
...Actually, all these scumbags need to do to defeat the "anti-twirl" is to use at least two more distort filters after the twirl that do *not* have a reversible direction. In this case, using Radial Blur in Zoom mode after running a Mosaic would totally frack the face where it couldn't be restructured. On the other hand, if the bastard had simply put a big black blot over his entire head, that would have been just as effective.
Now, if only there was an automatic death penalty for pedophiles, this would be a non-issue...
Yes sure, photoshop work perfectly..for mac user there is also a "photo rebooth" for Photo Booth
http://tinyurl.com/3xp9p3
You can undo everything to the extent that it just re-arranged information, as opposed to throwing information away. You just need to know the transformation function or be able to guess an approximation that is close enough. E.g. encrypting a file preserves all of the information perfectly, but you need the key to undo it (even for ROT13, but there the key is easily guessed.) Under these criteria, using standard Photoshop twirl is pretty much the stupidest thing you can do.
Before everyone goes condemning this guy, keep in mind that the camera adds ten boys.
Gone are the days where a pedophile could just drag a solid black patch over their face with MS Paint.