Slate has a great post up about using existing government databases to ID voters.
States maintain all kinds of data on citizens. Since Congress passed the Help America Vote Act in 2002 in response to the train wreck that was the 2000 election, they also maintain electronic voter registration databases....They argue that you can snap of a photo of a person at the polling place if they don't have a photo on record already and it can become part of that voter's record for the future. Seems like a great way to find a middle ground between ignoring the problem of voter impersonation on the one hand and preventing legitimate votes from being cast on the other.
Integrating those databases with existing databases, such as those maintained by state motor vehicle departments and public assistance programs, would make transcription errors in a voter's name or address obvious. Fewer voters would see their ballots challenged because of clerical mistakes.