[SOLVED] scrollable background picture in module

take a look at astridsolcer.nl when we scroll down you see a background picture which is in a module.
But i want to disable this foor iphone and tablet because on these devices the picture is way to big and the scrolling is not working at all
how can i fix this

In the template options, under Layout and Module Position, you can specify when the content should appear at which display size.