A bonus feature is the fact that this will also save you bandwidth because you won’t be using your server to serve the images, but WordPress’s!
There are quite a few of these CDNs available to play with but I want to talk about a free one called Photon. Photon is included in the popular Jetpack bundle and is extremely easy to use. It is worth noting that images Photon will only parse are images in posts/pages/custom post types and featured images.
Once, you have installed Jetpack on your site, you will need to link it to your WordPress.com account to activate the features. Once activated, Photon begins to work at once. That has to be the quickest CDN integration ever! Enjoy.