Re: Signing pictures -- how hard, how long?

[Jim McCoy <mccoy@ccwf.cc.utexas.edu>]

> From: "Alan (Miburi-san) Wexelblat" <wex@media.mit.edu>
> 
> At the Media Lab, some people have begun discussing the ease with which
> digital pictures can be altered.  One suggested way of ameliorating the
> problem is to have the original photographer append something like a PGP
> signature to the picture.
[...]
> One associated question has to do with the soon-to-be-productized next
> generation of high-end movie cameras.  These are all-digital at the source,
> so the question becomes: how hard would it be to build in digital signing at
> the source.  In theory, you'd like every frame (probably 70 fps in the
> ultra-high end HDTV cameras) to be signed -- how long would that take?

Well, the compression problem that others have mentioned is going to be one
problem, and an additional problem that occurs to me is that putting the
signature mechanism into the camera may not be the best locatoin for it.  I
do not know of any work that people would want to sign (e.g. would be worth
protecting from fraud) that did not undergo some post-processing...

One idea that sort of popped into my head if people want to do
post-processing signatures has to do with something else I remember hearing
about from the media lab:  you stack all of the frames together into a sort
of cube structure (like a deck of cards, for example) and then select and
sign random number of planes from different angles that intersect this
cube.  While not impervious to the fraud you are trying to detect, it does
create a much more managable detached signature (somehow I think that
creating 4200 signatures per minute is going to end up being viewed as a
bit unwieldy... :)  I think that you could even make the plane selection
ahead of time and then do it on-the-fly as the work is being filmed.  You
just keep track of which/where planes will intersect the frame being
generated and store the results of these intersections to a buffer that is
then signed before the storage media is ejected.

jim