The banner image here - https://www.google.org/index.html
Is responsive but also seems to scale within the image container
The image is a background image of a div that has attributes - data-parallax-effect, data-parallax-offest-x, data-parallax-offest-y and data-parallax-speed
As said, if you disable JS you get an insight into what aspects are/are not controlled by JS. The banner image is just a background set to background-size: cover. The only JS involvement is when you start to scroll, as you get a ‘parallax’ effect of the image scrolling at a different rate.