Cameras can be very discreetly installed in most places without being noticed. We at Boundary Surveillance Limited have installed a number of Smoke detector cameras with great results.  Please see picture below.

To anyone looking at the ceiling the smoke detector is just that, but its not, it is a high resolution colour camera with sound.

The PIR Alarm sensor is also very commonly used too It fits neatly in to the corner of a room looks like an alarm sensor but it's once more a high resolution colour camera with sound.  

Some business premises and other establishments prefer these type of cameras as they are less intrusive not in your face but blend in to the decor of its surroundings.

Realistically a covert or hidden camera can be installed into almost any object i.e. clocks, soft toys, books, plugs, light fittings etc etc.   

Examples:

	1/4" Panasonic CCD, high resolution colour covert camera. 380 TV Lines views down to 0.92 lux. 12v DC. AES, BLC, AGC. Dimensions (mm): 130 (Diameter) x 58 (H) Mounting bracket included Comes with a 3.6mm fixed lens. Built-in microphone for Audio pick up.
	Covert Camera in PIR Sensor  1/3" Sony CCD, Medium Resolution colour covert camera. 380TV Lines views down to 1 lux. 12v, 80mA. AES, AGC, AWB. Mounting bracket included.  Comes with a 3.6mm fixed lens.
	1/4"Sony CCD, 2 CAMERAS INSIDE 380 TV Lines views down to 1 lux. 12v DC, 220mA for two cameras 3.7mm fixed lens x 2