After searching the web, I found that serving images from sub-domain also improves the time because of the parallel downloading ability of browser. In this post I will tell you how to serve images from sub-domain and also redirect the older ones to the new ones.. October 2016 update You should use MaxCDN or KeyCDN for serving images from CDN under your website sub-domain.. Log in to your web-hosts CPanel, scroll down and look for sub-domains under domains and click on it... Enter name for the sub-domain i.e img example com, give the path of the folder. Go to Settings >> Media and enter the Full URL path to files with http in the beginning and no trailing slash in the end. You have set up sub domain for WordPress images and the older posts still use URL. Click on SQL from the nav-bar and enter the query given below, then click on Go. Other pages on the Web and Search engines might have indexed your images so it's better to redirect them to the new images. Do let us know if you prefer serving images from domain or you also create sub-domain to server images & files. .
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