Each &lt;img&gt; will be replaced with a &lt;picture&gt; tag that will also provide the WebP image as a choice for browsers that support it. Also loads the picturefill.js for browsers that don't support the &lt;picture&gt; tag. You don't need to activate this if you're using the Cache Enabler plugin because your WebP images are already handled by this plugin. <strong>Please make a test before using this option</strong>, as if the styles that your theme is using rely on the position of your &lt;img&gt; tag, you might experience display problems.