Nothing digital is unknowable

This from Threat Level:

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.

Follow the link. There are examples and more information — and the source code.