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Is the use of the Internet, sites like Flickr, contributing to the rise of faked images?
Krawetz: The Internet has a good amount to do with it, yes. It takes virtually no effort to modify--to cut and paste an image, to smooth things out. Even things like red-eye reduction--that's an image modification.
One of the things that surprised me is that when people render pictures--you know, a completely computer-generated picture--they usually don't just render it. They render it, then they bring it up in Photoshop to do digital manipulations to it. So it's not that it's just a computer-generated picture; it's an enhanced computer-generated picture.
Is that to bring in more textures?
Krawetz: Yes. To fix coloring. Maybe to paste in a background that's better than the one they rendered. Buzz Aldrin is a hybrid. The background is really from a NASA moon shot.
Images are composed of layers. I take it that each layer can be manipulated and put back together. Do the tools used leave behind any digital fingerprints?
Krawetz: You may not be able to track a tool to a person, but you can track a tool to a skill set. Tools definitely leave fingerprints. In fact, the last tool used is usually the easiest to identify.
Because the last tool used is the least manipulated?
Krawetz: Exactly. Photoshop stands out like a sore thumb. It's not that it's common, it's that it does some very distinct changes to the pixels before it saves them to a JPEG. That's not going into things like quantization tables or metadata information. Metadata can lie.
Fingerprinting--analogous to what you talked about at Black Hat last year?
Krawetz: Yes, analogous. My research is on antianonymity technology. I may not be able to tell you who someone is, but I can tell you about them. Last year, I was telling you about the words they use. This year, I'm telling you about the pictures they use. There are some repeating themes.
If they screw up on skin, they pretty much always screw up on skin until they learn to do it better. If they like to use Photoshop to put in particular edges or paste things in a particular way, you can actually see that sort of pattern. If you see a picture that is attributed to Photoshop for the Macintosh, then you know they're probably using a Macintosh and not a Windows box.
Going back to Buzz Aldrin and the British soldier in Iraq, is it the responsibility of the publications to guard themselves against manipulated images? If so, what can be done?
Krawetz: In my talk, I actually give some pointers for the mass media like Reuters. If they really want to publish pictures that have been unmodified, here's how you can tell. One way is to use quantization table fingerprinting.
If the picture claims to be from a digital camera, and the quantization tables, which are used for compressing the image, don't match the camera, then you know that it's been manipulated. If Reuters had done that, it would have caught the fake photos.
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