It’s not news that as-Sahab does a lot of post-production work on its videos. Click and scroll to see, for instance, the backdrops they chose for the 9/11 hijackers’ “video wills.” The news is how sophisticated they are about it. Using a process called error level analysis, a computer security consultant claims he’s able to identify which parts of an image have been added later digitally. Here’s his take on the Zawahiri video from last September:

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.

Krawetz was also able to determine that the writing on the banner behind al-Zawahiri’s head was added to the image afterward.

In other words, not only did they add the backdrop, they used After Effects or something like it to fake the Islamic inscription on a plain white sheet behind Zawahiri’s head. It ain’t CGI, but for modern cavemen that’s pretty slick. Krawetz is probably right, too, about them filming against an all black background. Here’s a still from an earlier video of Zawahiri where they didn’t bother to add a fake backdrop:

And here’s a still from one where they did:

Compare the more natural skin tone in those last two images to the first one, too. They’re obviously playing with the color to match him up with the color temperature of the backdrop.

Even more impressive is what they did with Gadahn. Spot the fake:

Error level analysis shows that the books in the lower right-hand corner of the image have a different error level than the items in the rest of the image, suggesting they were added later. In fact the books register the same error level as the subtitles and As-Sahab logo.

Further analysis also shows that the books have a different color range than the rest of the image, indicating that they came from an alternate source. Krawetz wasn’t able to determine what the books were but says if they were religious books, they might have simply been added to lend authority and reverence to the video. It’s also possible, he says, that such details could be added to a picture to send a message in code to al Qaeda operatives.

What’s left out there is that Gadahn and the computer are at the same “error level,” which means wherever he is, it’s probably not a cave.

Follow the link to see what the images look like under analysis.

Update: The more I look at it, the more I just can’t believe those books were added artificially to the Gadahn image. The fact that there’s a glare off the spine must be scrambling his analysis somehow.

Update (Bryan): For what it’s worth, it hardly takes “error level analysis” to conclude that Zawahiri’s background has been added digitally. His producers are using a virtual set, of the type you can buy here for a couple hundred bucks, and supering it behind him using nonlinear video editing software. My guess from looking at how the effect is laid in is that they’re using Final Cut Pro for the editing. That they’re using the black background isn’t surprising either. FCP’s color key effects can pull a decent key out of almost anything, as long as the background color is even (so can Premiere Pro’s, which is what I use in our productions) and isn’t too close to any color that the subject is wearing. Notice that Zawahiri usually wears bright, solid color robes. That makes for an easy key effect.

While we’re on the digital subject, the next time you hear a “terrorism analyst” *cough Mark Ginsberg say that al Qaeda’s videos show a sophistication that demands a roomful of high end gear, don’t believe him. It takes a desktop computer or a punchy laptop with firewire, a decent digital camera, decent portable lights, a mic, good editing software with keying capabilities and electricity. Al Qaeda could pack its entire studio in a single suitcase.