With BC, we got to using srcset and sizes together with BC's thumbnail parameters to generate right-sized images on the fly for various device/window sizes. Something like this:

<img sizes="(max-width: 1920px) 100vw, 1920px" srcset=" /images/sliders/slide-1.jpg?action=thumbnail&amp;width=480 480w, /images/sliders/slide-1.jpg?action=thumbnail&amp;width=576 576w, /images/sliders/slide-1.jpg?action=thumbnail&amp;width=768 768w,... (More)