Dumb question but... You're scrolling down the page and a bkgd image(s) appears static in a lower layer; Is that “no repeat” or some other script?
When you keep scrolling a different image appears static on a lower layer, and so on.
How do the images appear and are then “replaced” by new image?
Thanks in advanced!
Scrolling in Oklahoma!
So I suspect this is what you are looking for - Add scroll effects to background or browser fill.
Please note that to add scroll effects you need to have a fixed width (non responsive) layout.
Hope it helps.