If an intersection had a history of accidents involving pedestrians, photos would be useful in determining liability, for example. Please return to the curb. You can bet some bureaucrat would sign off on the idea, and not unreasonably. And you can bet it would work. Bureaucrats would point to the decrease in violations and injuries, and want more cameras.
Police departments cost a lot of money.
Cameras would allow more officers to do things that really counted, like catching murderers, instead of worrying about jaywalkers. Technology is hard to resist. And it improves. A year or so ago I did a story for a high-tech journal on a company called Photobit, which makes the light sensors for digital photography, scanners, and suchlike. They had found a way to reduce costs a lot.