The plate pictures are to collect money - there's an incentive to get that technology working right. In Illinois, open toll collection has reduced traffic jams a lot. Part of that driving by at 80MPH (yes the speed limit is 55, but almost everybody drives 70) and still collect the toll wasn't transponders, but getting the license plate number. If somebody doesn't have a transponder, the picture allows them to issue a ticket and collect the toll. It also allows them to bill rental car companies and get lots of money.
Car pool lanes - not so much money involved. There has to be some form of detriment to people driving there that don't belong. Police do that - sort of like driving on the shoulder - why doesn't everybody drive on the shoulder during traffic jams? Because there is a significant risk of a ticket.
On the other hand, there are places where you can pay to use the car pool lane - so license plate reading would make sense.