It is possible to configure a computer to support various devices with TWAIN interfaces. For example, the computer may have available a flat-bed scanner, hand-scanner, video capture board and other devices all with TWAIN interfaces.
When the Configuration, Set Default TWAIN Source... menu item is selected, a dialog will appear listing all the TWAIN devices currently available. The desired device for use with the Acquire feature can be selected. The dialog might appear like this:

This menu option will only be available of the TWAIN option has been activated.