Most car cameras come as a single camera package whereby the cam itself is fastened to the front windscreen and records the view of the oncoming traffic, the vehicles in front, and also the pavement area immediately in front and to the front-side areas - not areas perpendicular to the side doors.  On a motorway or dual carriage way, the front mounted camera will also record traffic ahead in lanes other than the one the car owner is currently occupying.  Below is a typical screen shot from a video taken using a front mounted camera at a traffic light controlled crossroad junction.

On the Motorway - through the windscreen.

Motorway driving can be hazzardous and there are lots of people flouting laws regarding car speed, tailgating and lane changing.  A front mounted camera can undoubtably catch out many of these types of misdemeanor level acts - and should they cause a danger to yourself or other drivers - or even an actual accident (fatal or not) - then the footage can be sent to the police for review. 

It should be remembered though that speeding would need careful consideration as the authorities use data as evidence from highly technical and calibrated equipment in case presentation to attain a conviction - and an amateur video of a speeding vehicle may not be considered as sufficient cause for prosecution.

In the motorway layout shown on the right, we can see the Four lanes of the carriageway, along with the sliproad - vehicles joining the motorway in an innapropriate or dangerous manner will be caught on film.
 

(Above - a typical scene from a front mounted car camera, the angle of the lens will determine how much detail can be shot on the left and right hand sides).

(Above - a front camera mounted correctly as per suggested guidelines will easily record traffic from Five lanes of a motorway or all the lanes in a dual carriageway).

What are the benefits of having a front and rear camera system?

With such good quality video data being collected from a simple front mounted system, it can be difficult to see why a rear view camera would be useful.  There are realistically a few valid points to take into account when deciding whether or not a rear camera is required for your purposes.

a) Short stay car park stop offs - a rear view camera will ensure capture of evidence should a driver hit the back of your car during a generally careless or otherwise poorly executed car parking manouver.  (note that a hardwire for security purposes or a long lasting internal battery would be required for this).

b) Rear end bumps - it is true to say that even if you only had a front facing camera, in most cases where a rear end shunt occurred, the video would show clearly that you were not at fault if this was the case.  If for example you were stationary and suddenly your car jolts forward - this would be accounted for on film and it would be obvious that your vehicle was not moving at the time of the impact.  If the offending driver decides to drive away - a rear view camera would more than likely capture the registration details allowing the insurance firms to trace the vehicle during a claim process.  You would not need to be stationary either to benefit from a rear camera in a rear car impact.

c) We have had one customer in particular who had made a claim to the police that she was being followed by a stalker who would pull out behind her during her commute to work, and harrass her on the road until she arrived.  A rear view camera was recommended in this extreme situation.

d) Instances of threatening and abusive driving, in particular on motorways where a vehicle is driving far too close for safe stopping distances, flashing their lights and trying to force you to pull over can be recorded.

e) Having a front and rear camera system such as the MI Witness could help in providing evidence in an incident which did not directly involve you or your vehicle, but may be useful as there were no other witnesses to describe what had taken place.