gewoon-jeroen
Hi
I checked your site view for mobile and image is showing max size already as its in the background.
There is black space as a min height is added.
Kindly add this code in override.css
@media (max-width: 640px){
#gkIs-gk-is-114 {
height: 100px;
}}
set the height as per needs to cover the black space.
Regards