Back to speeding and cameras briefly - privacy

[Pete Chown]

Richard D G Cox wrote:

> ... by checking for two "registrations" of the same number
> closer together in time than is consistent with the geographic separation.

Apparently Cambridge University Computing Service used to apply this
to terminal logons.  If you logged on in quick succession from two
terminals on opposite sides of town, you would find your account
suspended!

> Presumably the camera could digitally-sign any picture it recorded with a
> key held in a tamperproof sealed unit (but /will/ they do it that way?)

Apparently such cameras already exist -- one of the sales people here
was going to offer our services developing such a system, but we had
been beaten to it.

It's a shame I don't speed, because I could have lots of fun
developing devices for counteracting cameras.  Radar detectors are old
hat.  What you need is to make a small modification to the light above
your number plate.  You put a flash tube and a phototransistor in
there along with the bulb.

Now when the camera goes off, the phototransistor detects that there
has been a sudden change in the ambient light.  It triggers the flash
tube, resulting in a large overexposed blodge where your number plate
ought to go.

Of course, the system has to have enough power to fire twice in quick
succession.  I have been turning over a design involving a voltage
pump feeding two capacitors, with a flip-flop that decides which batch
of charge is dumped into the flash tube.  Once the system has fired
twice it then needs a delay while the two capacitors are charged up
again.

Perhaps I will write to Mr Straw and suggest that he installs one... ;-)

Of course, a system like this would also make it more difficult for
all sorts of cameras; not just speed ones.  I probably wouldn't have
published a design for a device to make speeding easier, but a device
that makes it harder for people to violate your privacy is another
matter.

-- 
Pete