A: EWWW IO includes two optimization methods, so you can use just one or both of them:
Compress API is the traditional method for optimizing the images hosted on your server. Your images are sent to our server, optimized, and then sent back to replace the originals.
Easy IO CDN optimizes images on-demand as your visitors view them. Images get copied to the CDN (as needed), optimized, and cached on the CDN system.
Both support various cloud-storage providers like Amazon S3 and GCS.
The latter, Easy IO, has a newer feature that allows you to deliver assets (images, JS, CSS) from additional domains which would allow you to optimize images hosted on your site AND those hosted elsewhere. It does depend on how those images are delivered. For example, if they are fetched via JavaScript, then we can't modify the URLs. But so long as the image URLs are contained within your site's HTML directly, Easy IO can deliver and optimize them.