Friday, October 12, 2007

A Scanner Darkly: Identification via Accidental Properties

It is the case that while it is "essential" properties that (by definition) define something, people very often identify types and individuals via a collection of "accidental" properties. For example, in a computer system, accidental (i.e. changeable) properties like name, address, phone number, etc are used to find/recognize/identify people even though they all can change thus producing the age-old problem of "identity over time".

Visually, people normally identify/recognize other people from their accidental attributes like face/hair/sex/etc. These can all be altered and not change their DNA or soul but that's what people normally use. If these change over time people use other attributes, or in the cliche science fiction scenarios where someone has been completely changed / possessed / transferred-essences-with-an-alien / etc, a shared set of secret shared knowledge is used. "Jim, it's really me, otherwise how would I know the name of your pet hamster on Rigel Seven?!" [Banks, Credit Cards, etc have recognized this and have started asking questions like "what's your favorite movie?" before letting you change your password.]

But for visual only recognition, say, for tracking someone through a crowd via a security camera, you are dependent on those accidental attributes not changing in real time. That is the premise for the "camouflage" in the movie "A Scanner Darkly". There is a cloak that constantly changes the appearance of every piece of the face/clothes, and this is illustrated via the rotoscoping and animation used in the movie. This would confuse automated tracking software and you would get lost in a crowd.

In thinking about this, though, I realized that people could still actually recognize the people in these cloaks BECAUSE WE DO IT WHILE WE ARE WATCHING THE MOVIE! A *real* cloak would be much more effective if it didn't change *pieces* of faces, but rather change whole faces at a time. It is easy to pick out the person in the funny changing cloak unless *everyone* is wearing one. Even then, humans can still keep track of who is who (short of a big crowd) because we track the various individuals at a "thing" level. I.E. I can see that there are some "things" in the room and when they move I can still tell who's who because despite their constantly changing "skin", they are still contiguous space-time blobs of matter (that walk a lot like people!).

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