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The traditional analogue camera has a resolution of approximately 0.4 megapixels.

Megapixel New IP digital camera technology is developing commodity camera systems at 3.1megapixel and cameras with a resolution of up to 16 megapixel are available in the market.
The advantage of using mega pixel (millions of pixels elements) cameras lie in the vast amount of image data captured.  This allows one camera to record in fine detail a much larger area than would normally be covered by a traditional CCTV camera.
So for public areas such as car parks, sports stadium, larger reception areas etc the benefits are obvious.
In the past low light performance compared with high end analogue cameras has been an issue, but advances in manufacturing technology is closing the performance gap.  
A number of factors hold back the greater adoption of the larger imager sizes. These include the requirement for lens design to match image resolution, storage considerations given the very large file sizes and bandwidth management.

Megapixel Comparison

Strategies for dealing with some of the above issues focus on only transmitting and storing relevant images that are automatically selected with the use of analytics built into the camera so that only alarms or exceptional events utilised by the system.

The operating concept is that using a wide angle lens offers video capture of a large area and also provides for high levels of retrospective digital zoom, making face recognition and capture of vehicle number plates easier.

A further development of the technology has led the use of new immersive cameras using panomorph lenses to provide a 360 degree view of an area, with appropriate software to ‘dewarp’ the image. This type of camera lens arrangement works best when ceiling mounted in the centre of a room or reception area, with the camera capturing images in all directions.
A variation on this technology is to use multiple cameras with specialist software which ‘stitches’ the images to make one endless scene.  This technology has been used extensively by the law enforcement community.