There are things I like about ALPR and things I don't like -- it's up to you guys to make sure it isn't abused. This technology could be abused without oversight.
Images are taken from cameras and matched against known "hot lists" of wanted people. Wanted for what? That depends. There's a list for expired plates (a.k.a. revenue generation - the selling point is that law enforcement will recoup the cost of the systems very quickly), stolen cars, murder suspects, missing people, sex offenders. There is even a notion of a "secret" list where the cops operating the system aren't even aware of what the analysts are looking for. These systems can also do geofencing -- if a plate for a known sex offender is spotted within a certain distance of a school, they're busted. Lots of stolen cars have been recovered via ALPR -- and remember most serious crime starts with the criminals obtaining a stolen car.
The system can also be used for internal investigations -- for instance there was a cop who was stalking his ex-wife who happened to have an ALPR. They pulled the capture history and her license plate came up multiple times. So he's busted.
Depending on how the system is set up they could store and back up the images and geolocations forever. There is current pending legislation regarding how long they can store data. The highway patrol can only store data for 60 days, most police departments have no such limitations. Update it looks like this failed--http://gizmodo.com/how-automated-license-plate-readers-threa...
Given enough mobile and fixed ALPR cameras the end result would be the same as having a GPS tracking device on everyone's car. I don't see why citizens should subject themselves to that long term data collection.
How about controls? Anyone querying the data leaves an audit trail behind. There are lots and lots of auditing and authorization levels built into the systems. That being said if something isn't configured correctly as was depicted here... http://money.cnn.com/2013/04/08/technology/security/shodan/
Something to note, this technology is out of the bag. In the future 3M which makes most license plates are going to be adding QR codes to license plates. http://www.tollroadsnews.com/node/6029 You won't really need specialty cameras.
Presently there isn't a national database for ALPR but they're working very very hard to make this a reality. It's up to you guys to make sure this technology is used with proper restrictions and oversight. As I heard out of the mouth of a salesman after a sale to a middle eastern country "Hey regimes are great for business!"