TWAIN_SetMultiTransfer(1)                  ' leave source open after Acquire
    If TWAIN_OpenDefaultSource() = 1 Then
        If TWAIN_GetDuplexSupport() > 0 Then   ' check for duplex support
            TWAIN_SelectFeeder(1)              ' turn on the document feeder
            TWAIN_EnableDuplex(1)              ' enable duplex scanning
            err = TWAIN_AcquireToFilename(0, "front.tif")
            If err = 0 Then
                err = TWAIN_AcquireToFilename(0, "back.tif");
            End If
        End If
    End If
    TWAIN_UnloadSourceManager()                ' unload TWAIN subsystem

• The key fact to know about duplex scanning is that TWAIN treats the two sides of a page as if they were two single-sided pages. When you turn on duplex, the scanner just transfers twice as many images.
• Some scanners that physically have a 'document feeder' don't admit it when queried through TWAIN. On those scanners SelectFeeder will fail, probably harmlessly.
• Some scanners can feed the next page while your program processes the last one - this can speed up batch scanning: See the TWAIN_SetAutoFeed function.
• A 'Source' (device) must be open when you call TWAIN_GetDuplexSupport.