[vpBG ]ViewportBackground – 1 per pass
allow to set viewport back ground per pass. You can control most settings in the Viewport Configuration dialog > Background tab.
You can use token to define background image path.
- Sync Animation Range – if you turn on this option, this pmodifier will adjust animation range to match to background range. If you want to have different animation range than background image range, turn off this option and use AnimarionRange pmodifier.
For all other options, please check 3dsMax help documentation.