[Cryptography] Photojournalists & filmmakers want cameras to be encrypted

[Jerry Leichter]

> 
>> Evidentiary is not a consumer camera. My SWAG is evidentiary is
>> less than 1% of high quality cameras and perhaps 100% of cell phones.
> 
> It's journos who are asking for this, and their cameras are definitely
> part of that 1%.  A reporter who can show that her footage isn't
> tampered can limit the degree to which people are able to credibly deny
> or discredit her story.
> 
> Now think evidence again.  Outside of journalism and investigation
> contexts, you don't know in advance which cameras are going to be used
> to record something that becomes evidence. A random college student at a
> demonstration takes footage of an incident of police brutality using
> whatever camera they happen to be carrying, and either is, or isn't,
> able to convince reporters/school officials that the incident wasn't
> faked, or convince police higher-ups that it can't be credibly denied.
I disagree.  This is all typical crypto talk, ignoring the realities.

It's trivial these days to produce a photograph - and possible, though right now much harder, to produce a video - that will appear to the untrained human eye to be genuine.  Even trained human eyes - of which there are few - can be fooled.

It's also trivial to argue successfully that the photo or video doesn't show what it appears to show.  How many videos of cops shooting a suspect lying face down on the ground being shot in the head draw the response "You can't just look at the picture, you need to understand the totality of the circumstances?"  Those responses are made exactly because, most of the time, they actually work.  (I'm not here commenting on the *validity* of the argument - just its effectiveness.)

On the other hand, when it's *really* necessary to check whether a photo or video has been tampered with, there are a variety of very sophisticated techniques to do so.  The editing technology we have is designed to fool the human eye and brain.  It's not designed to fool an analysis that examines stuff at the pixel level.  Sure, your eye may be unable to notice that part of the background has been duplicated to cover the hole left by removing a picture element; but it'll pop right out of an autocorrelation.  A trained eye *might* notice that the apparent light sources for two picture elements aren't at *quite* the same point; but light source analysis algorithms will spot this easily and prove that, no, those two guys were not actually standing next to each other when the picture was taken.

The real threat is *not* the fake pictures - which in important cases can be validated.  It's, ironically, exactly what the PBA spokesman brings up:  The selection of what to photograph and which photographs to present.  The individual photographs themselves are completely unmanipulated, but the narrative they present is false.  Defending against this kind of thing is not a technological problem - though in fact in many situations, technology *does* defend against it as a side-effect:  The broad distribution of cameras means that any selective presentation is likely to be answered by other pictures taken by many other witnesses.

One can come up with situations where a cryptographically verified "seal" on a picture - which to be useful must include the time and location - would be useful.  Consider photos taken by red light cameras.  Their location is fixed and known, and the photos contain a timestamp.  If there were reason to believe the photos were being manipulated, an cryptographic seal by a third party would be valuable.  (Right now, it seems unlikely anyone would bother.  The cheating around these cameras is done in much cheaper and easier ways.)  A more realistic scenario is the cameras put in place to monitor nuclear installations as part of treaty agreements to prevent diversion of bomb material.

But I'll contend that such situation are few and far between.  Sure, the necessary technology is pretty cheap these days.  If you're talking either pro-sumer of professional level camera equipment, or high-end smart phones, the additional cost would be minimal.  But I suspect interest would wane (if it were ever there) when people realized that they'd taken tens of thousands of shots - and no one had ever needed to check the signatures.
                                                        -- Jerry