Researcher’s Analysis of al Qaeda Images Reveals Surprises

Category people, Politics | Permalink | 2. August 2007

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Neal Krawetz, a researcher and

computer security consultant, gave an interesting presentation today at the Blac

kHat security conference in Las Vegas about analyzing digital photographs and video

images for alterations and enhancements.Using a program he wrote (and provided on the conference CD-ROM) Krawetz could print out the quantization tables in a JPEG file (that indicate how the image was compressed) and determine the last tool that created the image — that is, the make and model of the camera if the image is original or the version of Photoshop that was used to alter and re-save the image.

Comparing that data to the metadata embedded in the image he could determine if the photo was original or had been re-saved or altered. Then, using error level analysis of an image he could determine what were the last parts of an image that were added or modified.

Error level analysis involves re-saving an image at a known error rate (90%, for example), then subtracting the re-saved image from the original image to see every pixel that changed and the degree to which it changed. The modified versions will indicate a different error level than the original image.

You can see the difference in the two pictures (right) of a bookshelf. Krawetz added some books and a toy dinosaur to the original image — both of which show up clearly in the second picture after he’s completed the error level analysis.Bookshelf_and_dinosaur

But more interesting were the examples Krawetz gave of al Qaeda images. Krawetz took an image from a 2006 al Qaeda video of Ayman al-Zawahiri (above right), a senior member of the terrorist organization. The image shows al-Zawahiri sitting in front of a desk and banner with writing on it. But after conducting his error analysis Krawetz was able to determine that al-Zawahiri’s image was superimposed in front of the background — and was most likely videotaped in front of a black sheet.

Source and More : http://blog.wired.com/27bstroke6/

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