Hi,
There are a number of systems for UVSS (under vehicle surveillance systems). They have different features sets which vary the price.
The issue with these systems is that they take a video under the car and 'warp' it into a still image. They use an ANPR camera and link the pictures in a database and can check previous images of the same car for comparison (in case anything is added etc.)
You can try this website but this is one of the premier systems.
If you google 'under vehicle surveillance system' you will get a lot of companies. Some do in the road humps.
I have worked with these in the Middle East and one of the issues is keeping the camera lens clean due to the sand here.
Good luck!