Optical scan voting system
Types of optical scan systems
One technology used are optical mark recognition scanners where voters mark their choice in a voting response location, usually filling a rectangle, circle or oval, or by completing an arrow. During tabulation the optical scan voting system interprets the votes using "dark mark logic", whereby the computer selects the darkest mark within a given set as the correct choice or vote.
The ballot can be immediately tabulated at polling stations allowing for voters to be notified by the voting system of voting errors such as an overvote and can prevent residual votes. One such method can display a digital image of the ballot being submitted and allows the voter to review how their ballots are being read. This is known as a precinct count voting system. Alternately the ballots can be collected in the polling station and tabulated later at a central facility, known as central count voting system.
Electronic ballot marker
An electronic ballot marker (EBM) or ballot marking device (BMD) is an electronic device that can aid a disabled voter in marking a paper ballot. This device can allow for audio interfaces and still provide paper ballots.
Digital pen voting systems
Digital pen voting systems use ballots on digital paper which is recognized by a small camera in the pen while it is marked by the voter. The ballots are collected in a ballot box and the digital pen is returned to an election official for tabulation.
The technology was first used by the town of Menstrie, Clackmannanshire Scotland in their 2006 local community council elections. 
With this system there is no way for an automated recount.
Security and concerns
Optical scan voting systems are a form of document ballot voting system, meaning that there is a tangible record of the voter's intent (a paper ballot). Like traditional paper ballots these are vulnerable to electoral fraud and ballot stuffing.
One form of wholesale fraud possible with optical scan voting systems is during the recording of votes. Douglas W. Jones of the University of Iowa that if a potential attacker were to gain access to the voting system configuration files, they would be able to "credit one candidate with votes intended for another." He found these files are exposed in the computer system used to prepare the election, making them vulnerable to anyone setting up the election. The files are then transferred to the voting system using removable media, and "anyone with access to these media could potentially attack the system."
If an attacker is able to obtain a blank ballot (by theft, counterfeit, or a legitimate absentee ballot) the attacker can then mark the ballot her chosen candidates and convince (through intimidation or bribery) a voter to take the pre-marked ballot to a polling station, exchange it for the blank ballot issued and return the blank ballot to the attacker. This is known as chain voting/
Some suggest many of these well-known vulnerabilities can be effectively mitigated. Ballot stuffing may be resolved with incorporation of randomly generated ballot identifier for each paper ballot and capturing digital ballot images of scanned ballots as electronic audit.
Tabulation fraud and wholesale tampering can also be prevented by adding a cryptographic verification mechanism. This approach is mathematically based, and thus invariant to software attacks or breaches in chain-of-custody of the paper ballots. One such system is Scantegrity.
Benefits of optical scan voting machines
An advantage of these systems is that the voters don't have to learn to use a voting machine. Physically able voters can simply use pen and paper to mark their intent.
Optical scan voting systems can allow for manual recounting of ballots. Statistically relevant recounting can serve as a tool to detect or deter malfunction or fraud. Once an error in the counting process is suspected a full recount can determine the proper results.
- In the United States:
- AVANTE Precinct-Based Optical Scan Solution
- New Generation of Voting Machines in Germany
- Ulrich Wienser, Hacking the Electoral Law, Page 37ff
- Free and Hanseatic City of Hamburg: Bürgerschaft und Bezirksversammlungen werden 2008 digital gewählt (press release, German)
- Heise.de: Aus für den digitalen Wahlstift (German)
- Electronic voting 'world first', BBC News September 27, 2006
- EXAMPLE ATTACK DOCUMENTATION: Optical Scan Configuration File, Douglas W. Jones Sept 15, 2005
- The Harri Hursti Hack and its Importance to our Nation
- Security Assessment of the Diebold Optical Scan Voting Terminal (UConn VoTeR Center and Department of Computer Science and Engineering, University of Connecticut, October 30. 2006)
- Chain Voting, Douglas W. Jones Aug 26, 2005
- Comparing Tabulation of Paper Ballots using Optical Scanning Electronic and Tabulation of Direct Recording Electronic with Voter Verified Paper Ballots, AVANTE International Technology, Inc. March 1, 2007