to “rapidly scan the tags of passing vehicles, to help track down and arrest fugitive illegal immigrants.”
If anyone believes this government is interested in arresting illegals, they are deluded. Tracking them to award a passport and voter registration, certainly.
If you are illegal, you should not be licensed to drive, should not be the registered owner of a vehicle, should not be insured.
This is typical of Federal over-reach, from a department (Department of Homeland Security) that classifies returning serving military and military veterans as probable terrorists.
Colin Bastable 
They are attempting to come up with something to justify their existence. The entire department should be abolished if the government had the common sense to take such actions.