The purpose is to prevent forgery of documents. Actually, even more
   fundamentally, it is a way of saying "I was at this place at this time"
   - I don't believe there is any system which can do better than that
   (any kind of device-based fingerprinting would be a DRM scheme, and
   therefore flawed from conception.)
   I don't believe that these documents could be made to be
   self-verifying, although this is the sort of attempt being made with
   J3M. [1]CitizenMediaNotary proposes to make documents
   network-verifiable against retroactive forgery, but this is actually a
   different problem ("have we seen this before" rather than "where in
   spacetime was this created").
   Let's suppose a use case. Seems like we're about to have a nice little
   war in Syria, so let's use that. Suppose a citizen reporter creates an
   image of a bombed-out orphanage for impoverished nuns. Al-Jazeera wants
   to run with it, but can it be trusted? How do we know that this is
   actually an image from 2013 Syria, and not a previously-unpublished
   image from 2011 Libya, uploaded by a military agent?
   A geokey system would use network properties to assure that regions of
   spacetime have unique identifiers. These identifiers could then be tied
   to media, with a network protocol or J3M or something similar. Ideally,
   the handing out of these cryptographic identifiers would actually be
   done via satellite and not IPv4, as spatial IPv4 allocation isn't
   always accurate, especially with mobile phones. Also, the thought of
   there being geostationary microsats for the sole purpose of providing
   cryptographic spacetime assurances just gives me the sci-fi tinglies.
   Imagine little crypto robot oracles wizzing through space, beeping out
   random zeros and ones back down onto the planet!
   I guess the best we can do with this system is just narrow the "forgery
   surface" to people who are at a certain place at a certain time who
   have also preconspired to construct forgeries based on the keys
   generated by the oracle. This is not perfect, but it's better than
   nothing - assuming that we keep this limitation in mind.

   On Tue, Aug 27, 2013 at 8:57 AM, Lance Cottrell <[2]loki@obscura.com>
   wrote:

   I think we need to look first at the threat model you are trying to
   address. Is the concern that the photo's creator would fake the
   location of the photo?
   Is it that you want to make the location of the photo self-verifying if
   it is re-used?
   Do you want to simply be able to spot re-use and prove where the photo
   was actually taken?
   Something else?
   I think that a clearer definition of the problem will help identify the
   most appropriate solutions.
   --
   Lance Cottrell
   [3]loki@obscura.com
   On Aug 26, 2013, at 4:08 PM, Rich Jones <[4]rich@openwatch.net> wrote:

   This is a small, unfinished idea I had, but I'd be interested in
   hearing any feedback anybody here might have to offer. Normally we talk
   about cryptography to secure communications, but this is an idea rather
   about verifying the authenticity of media.
   [Quick backround: [5]OpenWatch is a global citizen media network using
   mobile phones as the basis for a free worldwide press. We care very
   much about the authenticity of citizen media, and have designed [6]some
   systems which attempt to improve the verifiability of citizen media.]
   The problem is that sometimes media artifacts are presented as a record
   of a current event, when in fact they from different events. An example
   of this was when images of a marathon race in Istanbul [7]were
   presented as images of the recent Occupy Gezi protests.
   Now, imagine the globe divided into a grid coordinate system, say
   100,000 units (or perhaps 2^32, if IP rather than physical address is
   to be used). Based on their physical location, reporters can contact a
   server and are assigned a key with which to sign or encrypt their media
   to. This then ties a media object to a physical space. This can be
   further improved to include both time and space by dividing a space-day
   into a number of units, suppose 1440, such that different keys would be
   handed out at different times of the day, thus further tying a document
   to a moment in time as well.
   Does anybody know if any systems like this have ever been discussed or
   designed in the past? I suppose this is somewhat similar to the
   RSA-keyfob system, although this allows for anonymous access without
   pre-arrangement as well.
   R

   --
   Rich Jones
   OpenWatch is a global investigative network using mobile technology to
   build a more transparent world. Download OpenWatch [8]for iOS and
   [9]for Android!

References

   1. https://github.com/Miserlou/CitizenMediaNotary
   2. mailto:loki@obscura.com
   3. mailto:loki@obscura.com
   4. mailto:rich@openwatch.net
   5. https://openwatch.net/
   6. https://github.com/Miserlou/CitizenMediaNotary
   7. http://twitchy.com/2013/06/01/debunked-photo-of-occupygezi-crowds-crossing-istanbul-bridge-is-a-fake/
   8. https://itunes.apple.com/us/app/openwatch-social-muckraking/id642680756?ls=1&mt=8
   9. https://play.google.com/store/apps/details?id=org.ale.openwatch&hl=en