Your first reference is video background (Not image).
16:9
In general width: 100% and height:auto make the image responsive (Fill up the width and maintain aspect ratio). If you upload 16:9 images this will work fine.
If you upload 4:3 or 1:1 and so on - and you want to “force” 16:9 + keep aspect ratio - you should use one line of custom css code - guide her:
Anyway, Add live-URL + read-only (Hard to know what is the problem by video).