What’s are some best practices for responsive images (e.g. for section headers)?

If you set background image to some tag inline, you still able to control it with css and media queries, !important is still working =)

<div id="image" style="background:url(image.jpg);">

!important still has priority over inline style and you can use in your media queries.

#image{
    background:url(another-image.jpg) !important;
}