Varying visible portion of an image

How can you vary the visible portion of an image when scrolled? For example, at

when you scroll to the woman with her hand up …

if you observe the top of the image and bottom of the image, as you scroll the white portion covers the top and bottom parts of the image. As if their is a white box with an opening that is moving on top of the image.

How can we achieve this in Saola?

Thank you!!!

Hi Shawn,

It’s the same as another topic you already asked.