So, this in and of itself isn’t all that interesting. But take a gander at this seemingly innocuous statement:
Local police [went] to recover a digital camera’s memory stick after [the photos] were tracked to Keys.
Heck, those photos could have been tracked down through any number of means:
- The ISP that Keys used to “upload” the photos may have cooperated.
- Keys may have been using an identifying account to whereever he posted them.
- He could have even watermarked them with “Copyright 2006 William Keys”.
Now read this:
Digital Cameras Have Unique Fingerprints
But the JPEG format tends to be the most ubiquitous image format for cameras and for the Internet. A part of JPEG is that it’s a “lossy” image format, meaning that you can dial-in how good you want the picture to look via its compression settings. If you alter the image by resizing it or changing the compression, will that alter the fingerprint? Of course, since the fingerprint is an artifact of the camera, these techniques would have to be done in “post processing” — using a software tool to make the changes on your computer after the images are retrieved. There are lots of techniques that are available for encoding a digital signature into an image, but according to Scheier’s source article, this looks like it’s a more genericized formula for identifying the make and model a camera that took the pictures.
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