Al-Qaeda's pixels popped?

There's nothing like a tiff between image processing experts to put a few extra pixels in your Monday.

Last week Wired.com ran a story in which a computer scientist claimed he could establish whether al-Qaeda had altered a video prior to posting it on the internet.

Neal Krawetz said he had written a program which would enable investigators to establish whether a background had been added to disguise the true location in which an al-Qaeda video was recorded, and, if the image had been altered, which editing software was used. (Of limited significance, perhaps, but interesting nonetheless.)

A video by a prominent al-Qaeda spokesman posted last year, had, for instance, had a desk, computer and some books added after the original recording, Mr Krawetz said.

A computer security expert at Cambridge University last week took issue with Mr Krawetz's claims, however, claiming that his analysis was flawed.

Mr Krawetz, who runs a computer security consultancy called Hacker Factor, told delegates at BlackHat security conference in Las Vegas that a technique called 'error level analysis' would enable investigators to establish which parts of an image had been altered or added later.

The altered sections appeared in a different colour once the analysis had been run, he said, adding that such changes could be used by al-Qaeda to send subtle messages to other operatives in code.

Dr Marcus Kuhn, who works in the Computer Laboratory at Cambridge, said, however, that while he agreed 'digital image forensics' was increasingly playing a role in intelligence gathering, the basis of Mr Krawetz's claims was incorrect.

Error level analysis could legimtimately provide insight into still images, such as JPEGs, but its application to moving images, known as MPEGs, was more problematic, Dr Kuhn said.

This was because the algorithms used for MPEGs were different.

"A tool designed for JPEGs will detect apparent manipulations in an MPEG image when in fact there was none," Dr Kuhn said.

"With JPEGs, detection is easy because the same compression level must be used across the entire image, and therefore evidence of different compression levels is evidence of manipulation. In MPEG, different quality levels in different parts of the image are normal, and not a sign of manipulation."

Dr Kuhn said he was writing to Mr Krawetz to raise this point and would await his response.

As will we. And, no doubt, the security services.

Comments

[KR]

Aren't they all created in the CIA labs anyway? That makes them all fake doesn't it?

[Joe]

I had the same thought as the prior poster: if the film was hacked, what leads one to believe al Qaeda hacked it's own film? Al Qaeda was originally created by the CIA to fight the Russians in Afganistan in late 1970s, early 1980s. Nominally, the story goes that the organization now bites the hand that brought it to life. But is that true?

[KRdunce]

Wow, you sound smart.

[Simon Arbuthnot]

KR is correct.

Everybody knows that Al-Quaeda are a creation of the CIA, that the twin towers were blown up by George W. to cover up his fathers involvement in The Philadelphia experiment with time, causing earth to be invaded by 12 foot high space aliens 40 years before the experiment took place. The space aliens are now building an inter-galactic craft in the bermuda triangle to get back home to their own planet.

The whole clash of civilisations thing is just a conspiracy to stop us finding out about it. The only people who know the truth are The Queen, Geroge W and George snr, Margaret Thatcher and David Ike.

[Gino]

How irresponible to claim the CIA made those photos.
I'm sure MI5 also made some of them.

[Fred]

Compressing jpegs with different levels of compression in different parts of the image has been around for at least 8 years.

[Adam]

The comments are more interesting than the post itself ;-)

[James Harrison]

How about the 12ft Aliens and do they also have the concept of religion as a socio-political weapon? Surely only a twisted genius alien lifeform with jpeg compression changing tecnology could pull of such a devious and evil move in order to take over the world?

If as suspected by Mr Arbuthnot the aliens have been around for 12 years this would have given them, by my indepth calculations (esimated using the decimal subtraction method) 4 years to invent multiple layered jpeg pixcel compression software and they have been busy manipulating everything we see since.

At this very moment they are also about to luanch not a spaceship from Nasau but "a multiple layed sound bite manipulator" ensuring that everthing we hear is also total nonsense. We are screwed. Thanks to SA for bring this to the worlds attention - it all makes complete sense now.

[Jonas M. Rogne]

I've compressed JPEG images with different amounts of compression in different areas of the image for a long time... This all sounds a bit strange to me.

There are many techniques to find out if footage has been altered, but "different levels of compression in different areas of the image" sounds a bit to simple.

[Ayala]

Anyone seen the nick berg video? edited by at least someone. (Maybe al Qaeda or maybe the cia.) Or the choppy audio on the bin laden confession tape as well as the somewhat fatter looking bin laden look a like? Im not with the nuts that think G-dub plotten 911, but both are clearly altered videos that have been used for political means by the administration.

[Mark S. M.]

I think that attempting to out-think the terrorist/ways/can be useless..it becomes the task of RAKING Leaves..you might attempt to begin a process to slow the falling leaves(impossible)..just rake the leaves..the Terrorist in my opinion have attempted to play w/the language and the Freedom of Speech/at such a point just leave matters to the greatest authorities..such as Inter-POL or the FBI..Scotland Yard..local police officials.."brain-storming" the terrorist war is foolish in more ways than/stopping the threat.

[Dr. Neal Krawetz]

The article states: "Dr Kuhn said he was writing to Mr Krawetz to raise this point and would await his response."

This is the first that I have heard of this. It has been 23 days since my presentation at Black Hat. I have yet to receive any contact from Kuhn.

For each of the images, I did not depend on any single analysis method. Instead, I used a wide variety of analysis techniques that all led to the same conclusion: the backgrounds were likely added using a chromakey replacement.