Backstretch

Backstretch is a jQuery plugin that adjusts a background image to fill the available space as the browser window changes in size. It's also capable of supporting a slideshow effect.

Backstretch loads images after other page content is loaded (i. e., after the DOMContentLoaded event is fired), so visitors won't have to wait for background images to load to use your site content. Even though background images don't impact the time it takes for your site to appear to load, they do increase the time to complete the loading process, and they do consume bandwidth to download them.