Commentary by DeepJournal
The expert on whose research ABC has based its article, was quoted in Wired earlier this month with even more intriguing information, namely that the logo from As-Sahab (the alledged media branch of Al Qaida) and the logo from IntelCenter (the US anti-terror watchdog) were added at the same time. Krawetz later withdrew this view he made earlier. This is a far cry from, as ABC does, writing about the possibility that the video's may have been doctored in order to carry messages by Al Qaida to its members.
Update: In this video Intel Center explains how As-Sahab produces video's.
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Maddy Sauer Reports:
Media and terrorism experts alike have remarked on the increasing sophistication of al Qaeda propaganda videos that continue to be released by the group's media wing, as Sahab.

One computer expert, however, has conducted extensive image analysis on many of the videos and concluded that in many cases the tapes were likely doctored to give a false impression of the speaker's location. 

Neal Krawetz, founder of Hacker Factor, a computer security and consulting firm, created a computer program which he uses to analyze screen frames from various al Qaeda videos, including those of al Qaeda No. 2 Ayman al Zawahri and American al Qaeda commander Adam Gadahn. His software suggests that in many cases the sophisticated backgrounds were likely added after the video of the speaker was recorded.

Photos: See What's Behind al Qaeda's Propaganda Tapes

By looking at the error levels of the different elements in the still frames, or JPEGs, he can tell which elements are older and which are newer. In other words, he can tell which areas of the video were modified more recently.

For example, in one video of Zawahri released in July of last year, he appears to be seated in a news studio complete with a backdrop of images of the World Trade Center attacks and hijacker Mohammed Atta.

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News commentators at the time remarked on how Zawahri, who many assumed to be hiding in a cave, was able to record a video message from a high-tech newsroom.

Krawetz, however, says that background was very likely added after Zawahri filmed his message.

"That's the fakest one so far," said Krawetz.

Krawetz found six different layers on one JPEG from that video, implying the various background components were very likely added after Zawahri recorded his message.

Krawetz says an even more visible clue occurs as the video itself plays, when there is a subtle shifting of the camera. The image of Zawahri appears to move side-to-side as if the camera is shaking while the background remains still.

In another video of Zawahri released in August 2005, the same summer as the bombing attacks on the London subway system, Zawahri appears outside of a tent with his trusted Kalashnikov behind him. At the time, some in the media remarked at the brazen message delivered in broad daylight just a few weeks after the London attacks.

Krawetz, however, notes that while the sunlight moves against the backdrop, the light levels on Zawahri's face never change. Once again, this implies the background could have been added after the video monologue was recorded. While it may appear he is staring into the sun because of the reflection in his eyeglasses, Krawetz speculates he was actually seated in front of a spotlight.

On the eve of the 9/11 anniversary last year, Zawahri and American al Qaeda leader Adam Gadahn released a video in which Gadahn praised the hijackers and their mission. On the tape, Gadahn is seen seated in a white room with a computer and books behind him.

After analyzing the image, Krawetz determined the books were at different error levels and a different color spectrum than the rest of the room, implying they were added when the subtitles and as Sahab logo were added to the video. Whether this was an attempt to send a message to followers, an attempt to hide something else in the background or served any purpose at all remains unclear.