How To Find Hidden Cameras.pdf

How to ﬁnd hidden cameras

Marc Roessler

marc@tentacle.franken.de

March 25, 2002

“We shall meet in the place where there is no darkness”

– 1984, George Orwell

Abstract

While it was easy to spot cameras twenty years ago due to their large size, this

has become increasingly difﬁcult during the last decade. Cameras have become

much smaller and consume a fraction of the power they did ten years ago. Due to

this, covert installation in nearly any imaginable place is possible. This paper will

show methods frequently used for hiding cameras as well as methods to detect and

locate covertly installed cameras.

Document available at http://www.franken.de/users/tentacle/papers/

1 Introduction

During the last few years the number of surveillance cameras has grown out of bounds.

Cameras have been installed in many public and semi-public places such as universities

[1], streets, supermarkets, gas stations, parking garages, cinemas, bars, shops, busses,

train stations and even discos.

About 25 million CCTV 1 cameras are estimated to be in operation worldwide at

the time of writing [2]. Some countries, notably Great Britain, are trying to fully cover

every corner of public life with cameras. The Privacy International CCTV page [3]

states that between 225 and 450 Million Dollars are spent on surveillance technology

in Britain per year, involving an estimated 300.000 cameras. These efforts result in a

person driving through the city of London being ﬁlmed at least once every ﬁve minutes

[4]. In the near future cameras may even be installed in all taxis, keeping an eye on

the passengers [5]. In Houston, Texas, about 400 cabs have been equipped with such

cameras [6].

1 Closed Circuit Television

It may not be obvious right away why it could be of any importance to anyone to

be able to locate hidden cameras. Some will reason that concealed cameras are more or

less exotic and thus knowledge on how to ﬁnd them is not necessary at all. Others even

consider interest in how to locate hidden cameras to border the criminal. Both parties

err, as shall be illustrated in the following.

Contrary to common belief, hidden cameras are nowhere close to exotic. In 1996

David Fletcher, chief executive of the British Security Industry Association, estimated

that employers were spending 12 million british pounds a year on covert camera equip-

ment to monitor their staff [7, p.49]. A survey conducted by the American Manage-

ment Association found that “33 percent of major U.S. ﬁrms say they tape employees

– overtly or covertly – to counter theft, violence, or sabotage” [8]. There have been

several reports of staff being monitored in changing rooms without their consent [9].

Subminiature cameras were even discovered by the author of this paper during treat-

ment at an oral surgeon’s practice: the camera was plastered into the ceiling next to a

ceiling light.

Subminiature camera modules are available for as cheap as $ 25 and even ready to

use wireless subminiature cameras can be legally bought. Ease of use and the drop-

ping prices highly contributed to the popularity of subminiature cameras. In effect

highly miniaturized cameras can be bought, installed and operated even by the aver-

age citizen lacking ﬁnancial resources and technical expertise. Due to this it is not

uncommon for subminiature cameras to turn up in places that are in fact neither public

nor semi-public. There is a growing number of reports of covert cameras spying on

unsuspecting persons in showers, bedrooms and changing rooms [11]. Knowing how

to ﬁnd covert cameras makes the voyeur’s job harder. Often even legally installed and

operated CCTV cameras are abused to peep on women for voyeuristic purposes. An

analysis showed that 15 percent of all targeted CCTV surveillances on women initiated

by the camera operator were for “apparently voyeuristic reasons” [7, p.129].

While there is concern that persons interested in ﬁnding hidden cameras may have

criminal intentions, there are legitimate reasons for such interest as well. One important

reason can be concern about privacy and personal freedom. Especially the growing use

of face recogniton software [12, 13, 14, 15, 16] is being strongly criticized [17]. There

is no way to distinguish cameras that are connected to face recognition systems from

those that are not. This is why persons who consider face recognition to touch their

personal freedom may choose to avoid surveillance cameras altogether. For instance,

they may decide to avoid stores that excessively use video cameras and visit stores that

do use signiﬁcantly less or even none at all. This is not possible unless the presence

of cameras is detected in the ﬁrst place. In countries with lenient privacy protection

laws video sequences captured by CCTV cameras may even be legally shown on TV

[18], no matter how humilating this may be for the affected persons (for an example

see [19]).

Some people might argue that cameras are easy to ﬁnd and this paper is therefore

unnecessary. Be assured that searching for covert cameras is in no way trivial. A mod-

ern camera including transmitter and batteries will easily ﬁt inside a box of cigarettes.

The Institute of Microtechnology of the University of Neuchatel (Switzerland) is de-

signing CMOS based subminiature cameras small enough to ﬁt inside a pen [20]. The

US company Given ® Imaging has even developed an “Ingestible Imaging Capsule”

for medical applications that is small enough to be swallowed. The capsule contains a

color camera, batteries and a transmitter [21]. Given the size of those cameras it should

be clear by now why naive attempts to ﬁnd cameras will not yield reliable results.

2 Types of cameras and lenses

The focus of this paper will be on electronic cameras. Subminiature photographic cam-

eras exist as well, but those are not as popular as electronic cameras. This is because

electronic cameras are more ﬂexible to install and operate. They facilitate real time

analysis and can be installed in places that are not easily accessible, since there is no

need for changing ﬁlms. On the other hand photographic cameras provide images far

superior in quality to those of standard subminiature video cameras.

Ancient electronic cameras used camera tubes [22, 23] to convert the virtual image

of the ﬁlmed object to an electronic signal. There are several tube designs [24] which

all suffer from drawbacks such as high power consumption, sensitivity to mechanical

stress, large size, short lifetime of the picture tube or high lag. Although there are still

many tube based surveillance cameras in operation, they are of low importance con-

cerning covert surveillance. Therefore this paper will focus on modern semiconductor

based cameras.

The camera does not need to be in the same room as the object under surveillance.

It is possible to connect the primary lens to the camera by means of ﬁbre optics [25],

which are very similar to those used for medical applications. One advantage of this

approach is that very little space is needed where the lens is to be installed. Another

advantage is that detection of the lens can be made more difﬁcult by using lens assem-

blies made of non conductive materials. Lenses prepared this way can not be detected

with metal detectors. Still another advantage is that otherwise inaccessible rooms can

be surveilled by feeding the ﬁbre cable through sewage or air condition ducts.

Fig. 1 shows some ways to obscure the camera’s lens. Lenses obscured as nail,

screw, or rivet head can be seen. Alternatively the lens may be masked as a shirt button

(not shown).

Fig. 1: Obscuring the camera’s lens (Picture courtesy of www.alarm.de)

2.1 CCD cameras

CCD 2 cameras are much smaller than tube based cameras and consume far less power,

typically two to ﬁve Watts [26]. Particularly interesting for covert surveillance are

subminiature CCD board cameras. Subminiature here means something like 32 mm

square and 10 mm depth including lens and electronics. A ”board camera” is a camera

fully contained on a single circuit board including camera optics and all the electronics

needed for generating the standardized video signal.

CCD cameras are available as monochrome (i.e. black and white) and (more ex-

pensive) color versions. Several lenses are available such as tele (“zoom”), ﬁsheye

(wide viewing angle) and pinhole. Pinhole lenses are small diameter ﬁsheye lenses of

typically 2 mm or less in diameter. Pinhole lens cameras are particularly interesting for

concealed surveillance applications because they can ﬁlm through very small holes 3

and even through light-weaved cotton. Monochrome cameras usually are more light

sensitive (0.5 to 2 Lux) than their color counterparts (about 3 Lux). A pinhole black

and white CCD board camera can bee seen in Fig. 2 at the right side.

Historically the major advantage of CCD cameras has been superior picture quality,

but CMOS cameras (see below) are catching up rapidly. Compared to CMOS cameras,

the CCD camera’s disadvantages are large size, high power consumption and bloom-

ing. Blooming means “leakage” of bright pixels to neighbouring pixels. Bright parts

of the picture such as light sources facing the camera will look smeared [27]. An-

other disadvantage is that CCD cameras can only be operated at temperatures below

approximately 55 degrees celsius [28]. In addition they have rather low dynamic range

compared to CMOS cameras. This means that CCD cameras will fail to record very

brightly lit and very dark objects at the same time. Bright parts of the picture will be

overexposed while darker areas will only show black [28].

Black and white CCD cameras are sensitive not only to human visible light but also

to radiation in the near infrared (IR) spectrum. This can be demonstrated by having the

camera “look” into an active IR remote control as used for most TVs and VCRs. IR

remote conrols use light with a wavelength of approximately 900 nm. Light of this

wavelength is invisible to humans but can be detected by black and white CCD cam-

eras. The IR pulses that are emitted by the remote control can be seen as a ﬂashing light

on the video monitor. This offers some interesting possibilities. If an artiﬁcial source

of IR radiation is supplied, monochrome CCD cameras can be used without any hu-

man visible light source. In effect such cameras can ﬁlm in “complete darkness”. The

mentioned IR emitter can comprise several IR-LEDs 4 grouped together, for example.

Another possibility is to use a modiﬁed halogen ﬂoodlight with an IR pass ﬁlter ap-

plied to it. In some multiplex movie theatres there are CCD cameras and IR ﬂoodlights

mounted at the ceiling above the screen, facing the audience. This enables personnel to

take a look at what the audience is doing even in complete “darkness”. Color cameras

are sensitve to IR radiation as well, but in practice IR sensitivity is too low to be of any

use.

2 Charge Coupled Device

3 In many cases 1 mm is sufﬁcent.

4 Light Emitting Diode

2.2 CMOS cameras

Another type of camera which has shown up recently in the catalogues of electronics

vendors is based on CMOS 5 technology. CMOS cameras were quite rare a few years

ago but are now gaining ground with consumer products such as small handheld de-

vices and webcams. They are available as monochrome and color version with several

lenses such as pinhole and ﬁsheye to choose from. Subminiature CMOS cameras usu-

ally do not come as board cameras but rather as modules packaged in small plastic

cases, as can be seen in Fig. 2. They are about half the price of CCD cameras, less

sensitive to electrical distortions, may be operated at temperatures ranging from -40 to

+120 degrees celsius [28] and consume far less power (20 to 50 mW) than their CCD

counterparts [29, 26]. They can be built much smaller than CCD cameras as major

parts of the necessary circuitry can be built directly onto the substrate that carries the

light sensors. Just like CCD cameras they are sensitive to IR radiation [23]. In addition

they have a high dynamic range [28], i.e. very bright objects and very dark objects can

be recorded satisfactorily at the same time.

CMOS cameras have disadvantages as well. Because each pixel comes with a

piece of circuitry of its own which consumes room and light, CMOS cameras are not

as light sensitive as CCD cameras [30]. Another disadvantage is the lower picture

quality, as the individual pixels are quite noisy. There are APS (Active Pixel Sensor)

CMOS cameras available which attempt to cancel out the noise, but those are more

expensive than the standard PPS (Passive Pixel Sensor) cameras [30]. CMOS cameras

do have signiﬁcant advantages over CCD cameras in regard to noise if large pixel arrays

(megapixel arrays) are to be built [31].

CMOS imagers are likely to supersede CCD imagers within the next few years,

especially on the consumer market. For more detailed comparisons of CMOS and

CCD cameras see [32].

Fig. 2: CMOS (left) and CCD (right) pinhole camera

5 Complementary Metal Oxide Silicon

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