March 05, 2007

Digital imaging goes to court

CNET reported recently on a court case that involved image authentication software as well as human experts, both seeking to distinguish unretouched photographs from those created or altered using digital tools.  After disallowing the software, written by Hany Farid & his team at Dartmouth, the judge ultimately disallowed a human witness, ruling that neither one could adequately distinguish between real & synthetic images.  The story includes some short excerpts from the judge’s rulings, offering some insight into the legal issues at play (e.g. "Protected speech"–manmade imagery–"does not become unprotected merely because it resembles the latter"–illegal pornography, etc.).

As I’ve mentioned previously, Adobe has been collaborating with Dr. Farid & his team for a few years, so we wanted to know his take on the ruling.  He replied,

The news story didn’t quite get it right. Our program correctly classifies about 70% of photographic images while correctly classifying 99.5% of computer-generated images. That is, an error rate of 0.5%. We configured the classifier in this way so as to give the benefit of the doubt to the defendant. The prosecutor decided not to use our testimony because of other reasons, not because of a high error rate.

The defense argues that the lay person cannot tell the difference between photographic and CG images. Following this ruling by Gertner, we performed a study to see just how well human subjects are at distinguishing. They turn out to be surprisingly good.  Here is a short abstract describing our results. [Observers correctly classified 83% of the photographic images and 82% of the CG images.]

Elsewhere in the world of "Fauxtography" and image authenticity:

[Update: PS--Not imaging but audio: Hart Shafer reports on Adobe Audition being used to confirm musical plagiarism.]

Posted by John Nack at 3:50 PM on March 05, 2007
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