Garling Gauge

Is it Live, Or is it Al-Qaeda?

2006 video of Ayman al-Zawahiri posing before a false background

Technology exposes terrorists’ cozened cinema

Reported on Wired by Kim Zetter, researcher and computer security consultant Neal Krawetz unveiled a new program today enabling digital photographs and video images to be analyzed for alterations and enhancements.

Presented at the BlackHat security conference in Las Vegas, the program Krawetz wrote creates quantization tables in a JPEG file to determine how the image was compressed, ascertaining the type of camera or Photoshop version last used on 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.

Krawetz presented an analysis of al-Qaeda videos, revealing what parts of the images were added in later, such as the background to the al-Zawahiri video above:

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.

The writing on the banner was also added to the image afterwards.

2006 video images of Azzam al-Amriki with Error Level Analysis

By using error level analysis on the above video image, Krawetz revealed that the religious books have the same error level as the subtitles and As-Sahab logo, implying they were inserted later into the video.

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.

The books also have a different color range - another indication of technical slight of hand.

The article’s concluding sentence is hair-raising, and should give Homeland Security pause: