Schneier on Security

Clive Robinson • March 13, 2014 8:44 AM

@ Figureitout,

I’m wondering though how you evade CCTV on stoplights, buildings, and increasing all sidewalks/ roads in cities.

The first thing to note is a camera can only see what you chose to reveal to it in it’s presence.

So step one is not to be in a cameras locality or field of view. To be able to do this means knowing where the cameras are, which generaly means first looking for them to locate them, which is not that easy. But it is also self defeating because the “looking” process tends to stand out as “suspicious activity”.

So step two is to know what a cameras weakness is and play to those not it’s strengths and this is possibly the better way to go.

No matter how cheap the camera hardware is they are expensive to instal, maintain and operate, thus they are actually quite scarce items in reality and those that pay for them generaly want to get the best value for money they can. This means they are usually positioned to get what the owner considers maximum benifit. Thus at “choke points” or high up to give maximal coverage of an open space. And this has consiquences on their utility. As a rough rule of thumb the sensors in all cameras have limitations due to mass production methods and the laws of physics which for single sensor cameras defines the trade off between sensitivity and resolution [1] which in turn effects the optics used to foucus the light onto the sensor which gives another trade off between resolution and field of view. That is the greater the field of view the less the resolution, which brings in another trade off, when it comes to wide area coverage, the general trade off is to put in stearable cameras with variable magnification optics to zoom in on a point of focus. And this is a major Achiles heel of CCTV, which also makes it expensive to use as it requires a human operator currently.

Humans as we know have many failings, not the least of which is the ability to concentrate especialy on images that are “busy” and or of low contrast and brightness. This often causes camera operators to zoom in much further than required to reduce the busyness of the image.

Another failing of humans is what our “monkey brains” tell our concious minds. If you look at a list of human basic needs you will find that they effect camera operators, so what the monkey brain considers a threat, sex, etc potential are going to grab the operators attention.

From this it can be seen that you want to avoid places that are “choke points” where cameras are fixed field of view and often direct to recording equipment and not humans and you also want to avoid “quiet times” when you are more likely to be the only point of intrest to an operator.

You should also consider times when light levels are low and images “busy” in terms of lots of shadow and bright spots such that the contrast range is high to the camera causing the contrast to be turned down. Likewise inclemant weather causes image issues so are times when operators are going to be less effective. For instance wind blowing garbage around creates a “busy” image which operators monkey brains will be distracted towards.

Basic army training manuals will tell you about shape, shadow, shine, colour, contrast, movment, etc that if used carefully will push you away from the forground and into the background. If you don’t trigger the monkey brain in a busy environment that is triggering it, then you are effectivly invisable to the monkey brain and thus the concious mind unless specificaly focused already.

[1] This is one of the reasons multiple sensor cameras to be used from drones etc are being developed and deployed. However these multi sensor cameras cause other problems not least of which is the bandwidth required in both communications and storage [2].

[2] One solution to bandwidth issues often touted is compression, the reality of this is if you reduce bandwidth you either lose information or concurancy at some point depending on how “busy” the image is.