A new cryptographic voting system pioneered by MIT was implemented in Takoma Park, Md., earlier this month. The system, called Scantegrity II, works with optical-scan ballots and technology. The voter marks his or her ballot, and notes the code numbers revealed as the bubble is filled in. After the election, voters can log in to the city's election site, enter the serial number of the ballot and check the codes of their selections against the candidate codes to ensure their votes were tallied correctly. According to MIT, any attempts to tamper with the vote are easily detected. See more detail here as to how the system works.