Computer security consultant Neal Krawetz showed a different way to look at al Qaeda images in a talk at the BlackHat security conference in Las Vegas. He looked at the quantization tables in a jpg file to how the image had been compressed. Wired's blog explains:
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.
Krawetz examined an image from a 2006 al Qaeda video of Ayman al-Zawahiri and reckons it was videotaped in front of a black sheet; a desk and banner were added later.
