Rocket Lazy Load is a simple but powerful plugin with a tiny (less than 2kb) lazy load script without any jQuery and others libraries. What all this script does is, it displays images on pages only when they are visible to your user’s eyes i.e. only when show up on screen with down scroll. Hence, this trick reduces the number of HTTP requests mechanism and improves your website’s loading time.
Simply install and activate Rocket Lazy Load plugin. Upon activation the plugin starts working on thumbnails, all images in a post content or in a widget text, avatars and even smilies. No options, just activate and the plugin takes care of everything. Same script is used by WP Rocket plugin cache: wp-rocket.me