What is required to ensure confidentiality when using a fax machine for transmitting III information?

To ensure confidentiality when using a fax machine for transmitting Interstate Identification Index (III) information, it's vital to use a secure line. A secure line guarantees that the information being transmitted is not intercepted or accessed by unauthorized individuals during the transmission process. The nature of sensitive data, like that found in the III, necessitates high security measures, given that it may include criminal history or personal information.

Using a secure line supports maintaining the integrity and confidentiality of the information throughout the transmission, which is essential in law enforcement and criminal justice settings. While other options may seem relevant, they do not address the key factor of ensuring the security of the transmission itself, which is critical to protecting sensitive data.