Comment Answering OP's questions (Score 1) 483
I'm disappointed that there have been so many comments suggesting anything but help on speed camera (possibly because they are unpopular devices). Speed cameras do have the potential to reduce speeds around accident black spots, assisting in the number of injuries and fatalities. Speed cameras can also be considerably cheaper to implement than traffic lights and provide a revenue stream to fund maintenance.
In terms of preventing disputes of pictures taken by cameras I would suggest that you look at techniques used in the UK. There they take two photographs of any speeding vehicle at precisely timed intervals. There are marking on the road to show distance so the two images can be used to prove that the vehicle covered the distance stated on the ticket.
Another item I would recommend is that all digital evidence is signed with a digital signature to show it has not been tampered with. In Australia md5 hashes were used to show an image had not been tampered with, and that allowed someone challenge the ticket successfully in court as the defendant was able to demonstrate that someone could have easily replaced both the image and hash (as anyone can create an md5 hash, but a digital signature requires the private key).
Tamper proofing is also very important (expect attacks on cameras with many items). I strongly recommend mounting cameras on high poles (at least 2.5m, basically beyond the swing of a baseball bat) to reduce vandalism.
Mobotix make some excellent cameras, and while they are not designed to function as speed cameras they are programmable and offer and excellent api. Additionally, they function extremely well in bad weather conditions due to having no moving parts. They also make vandal resistant cameras and I have personally hit one of their cameras repeatedly with a sledgehammer and it continued to function throughout. I've also used them without issues in the top end of Australia where the temperature can exceed 45C and there is often high humidity.