Lazy Optimization plugin is the first ever WordPress plugin to lazy load background images that are in external CSS files.
Lazy Optimization plugin works on top of Autoptimize plugin and is used to lazy load background images that are present in Autoptimize external CSS files.
Lazy Optimization plugin replace all the background images that are in Autoptimze external CSS files with a dummy image and when the element with the background image comes in viewport it’s original background images gets loaded.

Dependices Autoptimize.