1. Grab image1 with time stamp & sonar range stamp & AHR stamp
2. Grab image2 with time stamp & sonar range stamp & AHR stamp
3. Locate a feature1 in image1
4. Locate feature1 in image2 if not present && you tried 3 times repeat step 3
5. Calculate velocity vector based on difference in timestamps, sonars and AHR data.
This shit is HARD.
http://stackoverflow.com/questions/4872570/find-speed-of-vehicle-from-images