mabujo

Featured Image Sharpen Up makes a tiny version of your featured post image and places it in the head of the page. 
As you scroll down the page, some JavaScript lazy loads the featured images in the background and replaces the tiny images as the full images are loaded.
You may have seen a similar effect used for images on medium.com.
Created on WordPress 4.4, but should work on earlier versions. 
Tested working on all Twenty Sixteen, Twenty Fifteen, Twenty Fourteen, Twenty Thirteen, Twenty Twelve and Twenty Eleven themes. Should work on other themes, but may need CSS adjustments, depending on theme handling of featured images.
Uses jQuery.Lazy(); (http://jquery.eisbehr.de/lazy/) and Hugh Lashbrooke’s plugin template (https://github.com/hlashbrooke/WordPress-Plugin-Template)
Plugin page : <a href="https://mabujo.com/blog/featured-image-sharpen-up-wordpress-plugin/" rel="nofollow ugc">Featured Image Sharpen Up plugin @ mabujo</a>

Featured Image Sharpen Up

This plugin helps increase the page loading speed of your site by replacing featured post images with a small inline image, and lazy loading the full  …

kvasnyi

skylineweblab

Lazy Load by SWL is a fast and lightweight delayed content loading jQuery based plugin for WordPress 
It’s designed to speed up page loading times and decrease traffic to your users by only loading the content in view.
<h3>Credits</h3>
<ul>
<li>Based on jQuery Lazy Library (http://jquery.eisbehr.de/lazy/) by Daniel ‘Eisbehr’ Kern, licensed under MIT.</li>
</ul>

Lazy Load by SWL

Lazy Load by SWL is a fast and lightweight delayed content loading jQuery based plugin…

Featured Image Sharpen Up vs Lazy Load by SWL