>> You could have the camera write a digital signature and make it really 
>> awkward to get at the encryption key [which must, necessarily, be 
>> present inside the camera somewhere]. But when, if you have an image 
>> in RAW format, I would imagine it's fairly easy to fake anyway.
> 
> And then what? Everybody at Canon can forge image signatures?

Yeah, but that's have no motive.

A much bigger problem is that it only takes one single person to 
successfully extract the key from a single camera and put that on the 
Internet, and all signatures become worthless.

Alternatively, perhaps if every camera had a unique key... (Then you'd 
be able to prove which camera took the shot too.)

> It's like your signature on a contract. Very rarely does someone try to 
> claim that their signature isn't really what's on the contract. That's 
> why the credit card companies don't care if you sign your name with a 
> picture of  mickey mouse or something. The actual signature doesn't 
> matter, only that you wrote on the line that says "by writing on this 
> line you agree to pay."

Heh. I heard some guy got given a cheque and the customer forgot to 
actually sign it. The bank handed over the money anyway. (WTF?)

>> Most people don't just happen to have a Nikon DSLR in their pocket 
>> when they witness a robbery. They shoot people with camera phones and 
>> stuff.
> 
> Well, it's also police photographing evidence. It's not like you can 
> leave the bullet casings on the floor until it's time for the trial.

Well, that's another matter entirely, yes. I think you have to take 
police evidence as valid, because if the police themselves are trying to 
frame somebody, there's not a lot you can do in a courtroom...

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