I came upon this 2007 news source which is not covered on ATS before. It raised some pretty serious questions. Find out:
Neal Krawetz, a researcher and computer security consultant, gave an interesting presentation today at the BlackHat 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
You can see the difference in the two pictures (below) 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.
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),
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.
Krawetz was also able to determine that the writing on the banner behind al-Zawahiri’s head was added to the image afterward. In the second picture
above showing the results of the error level analysis, the light clusters on the image indicate areas of the image that were added or changed. The
subtitles and logos in the upper right and lower left corners (IntelCenter is an organization that monitors terrorist activity and As-Sahab is the
video production branch of al Qaeda) were all added at the same time all have the same error level, while the banner writing was added at a different
time has a different error level, likely around the same time that al-Zawahiri was added, Krawetz says. (See 2nd update below.)
Even more interesting is the analysis he conducted on another 2006 video image of Azzam al-Amriki showing him in a white room with a desk, computer
and some books in the background. 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
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
For those of you who asked for Krawetz’s program, you can view the
source code here.
You can also view his BlackHat presentation here (PDF)
. For those
of you who think the software is better used to catch media manipulations of photos and video, Krawetz did present examples of these in his talk.
And to "Ann" who commented that she doubts al Qaeda would put subtitles on a video, As-Sahab, the logo in the lower left corner of the two al Qaeda
videos is the production arm of al Qaeda. Yes, the organization has its own media production team.
2ND UPDATE: I quoted Krawetz as saying that the evidence indicates that the IntelCenter and As-Sahab logos were added to the al-Zawahiri
video at the same time. Ben Venzke of IntelCenter says his organization didn’t add the As-Sahab logo. He points out that just because the error
levels are the same for two items in an image, that doesn’t prove they were added at the same time, only that the compression was the same for both
items when they were added.
I was finally able to reach Neal Krawetz at the BlackHat conference to respond to the questions about the IntelCenter and
As-Sahab logos (Krawetz doesn’t have a cell phone on him so finding him at the conference took a while). He now says that the error levels on the
IntelCenter and As-Sahab logos are different and that the IntelCenter logo was added after the As-Sahab logo. However, in a taped interview I
conducted with him after his presentation, he said the logos were the same error levels and that this indicated they were added at the same time.
Additionally, after I’d written the first blog entry about his presentation, I asked him to read it to make sure everything was correct. He did so
while sitting next to me and said it was all correct. He apologizes now for the error and the confusion it caused.
Was Neal Krawetz telling the truth first time or did he really made an honest mistake? You decide!