Path: utzoo!utgpu!news-server.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!rutgers!apple!limbo!taylor
From: jgk@osc.osc.COM (Joe Keane)
Newsgroups: comp.society
Subject: Re: Manipulation of Courtroom Evidence
Summary: With a PC and some skill you can make very good fakes.
Keywords: forgery, photographs, speech
Message-ID: <542@limbo.Intuitive.Com>
Date: 17 Mar 90 20:18:16 GMT
Sender: taylor@limbo.Intuitive.Com
Organization: Object Sciences Corp., Menlo Park, CA
Lines: 27
Approved: taylor@Limbo.Intuitive.Com

Ludovic van B writes:

> Maybe the only way to make sure a photograph is valid as courtroom evidence
> is to ask for the negative. I feel this is - still - impossible, I mean
> tampering with negatives or creating entirely false ones.

If you can create a perfect fake photograph, complete all the artifacts you'd
have in a real photograph, it should be easy to make a negative from that.  I
don't see how you could tell this from an authentic negative.  Maybe there's
some aging process in the negative which lets you date when it was exposed or
developed?  I don't know of any.

> On the other hand, proving that a tape recording is 'modified' or entirely
> false might be easier, I don't really know. Does anyone know whether computers
> can say with total accuracy that a voice is artificial? (Imitated is a piece
> of cake to detect) Even though the recording might be 'corrupted', i.e.
> 'noisy'? I'd like to know.

If you have a large amount of authentic recordings of some person's speech,
you can make a recording of him saying anything you want.  And if you're good,
there would be no way to tell that he didn't actually say it.  In many ways,
this is even easier than making a false photograph.  The only hardware you
need is a PC with A->D and D->A converters.  It might take a week of number
crunching, but that's not a big problem.


Joe