Finding a way to inconspicuously get into the carpool lane without actually having a passenger can be a lucrative business and is also a source of great consternation to drivers legally allowed to be in the lanes. There have been a few attempts at policing carpool lane usage, but this is the first time that we've seen electronic trickery "smart" enough to tell the difference between real people and dummies. Using infrared signals, U.K. cameras being tested in Leeds are able to "see" the blood and water that is present in a human body and can distinguish between real people and fake bodies.
One potential problem is that some cars, namely certain hybrids and CNG vehicles, are allowed in the carpool lanes with only one passenger. The cameras would need to be programmed somehow to allow these travelers to drive alone without being ticketed.