Buckinghamshire CC ANPR cameras

John Wilson tugwilson at gmail.com
Mon Jan 9 17:32:04 GMT 2012

On 9 January 2012 17:21, Peter Fairbrother <zenadsl6186 at zen.co.uk> wrote:
> If all they want to do is monitor traffic levels and average journey times,
> then a short - say 10 bit - hash is appropriate. Still not private, but it's
> enough to get the needed data without overly complicating things.
> If the hash function is such that the hash changes say every day, or better
> for every rush hour, then very little private data would be available.

Quite so. However they started with an 18 bit hash and then moved to
24 bits. It looks like they want to have some collisions (so that they
can claim it's not personal data) but to have as small a number as
possible to allow them to see long term patterns.

I'm not against this. I can see that there my well be significant
advantage for a planner to have access to detailed travel information
over an extended period of time. My problem is that this is
effectively personal data and they are using sleight of hand to deny
that and hence dodge their responsibility for handling it carefully.

John Wilson

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