[karambahh]

See Mappilary work on this area. Although they work on static pictures, I wouldn't be too surprised if their work could be succesfully applied to real-time video.

Another area you can explore are commercially available units. French police use on board license plates readers which seem to be quite fast (at least when you watch the french equivalent to the "cops" tv show).

http://www.teb-online.com/fr/analyse-images/lapi-lecture-aut...

LAPI(Automated Reading of License Plates) is the acronym you want to look for. I think several hardware and software manufacturers equipped different police units so if you're really interested, you'll be able to find several datasheets and derive a reasonable minimum computing power from them.