As others have mentioned, the TV CSI shows can dramatically exaggerate what is possible.
But, enhancing a video to get a license number is a lot more possible than enhancing a still image. This is because, a video is composed of a LOT of still images shot in sequence. So, it is possible to aggregate the many pictures in a way to increase the resolution. Sort of the way pixel shifting can be used in a projector to enhance the resolution to 4k, even if only a standard HD imaging system is used.