Although you can use built in media manager of wordpress, using OneDrive can be another option.
You can consider using OneDrive if you are short f space on your hosted server or your free account as well. OneDrive offers 5GB of free storage. Please follow following simple steps to use OneDrive as CDN for media files.
Step#1. Create an account on OneDrive and upload an image.
Step#2 Select that image and use click on embed option as show in below screenshot (btw, this image is hosted on OneDrive)
Once you select on embed, you need to click on generate code. This option is at right side. On the same screen, you can choose the filesize to be shared.
Step#3 Now finally to insert images into your wordpress post, you “add Media” option but select option, “insert from url”
Once done, you are all set.
Before you start using, I must tel you disadvantage of this option is that, if wordpress is blocked at some place, these images wont be visible. I was using google drive as CDN but later found that google drive is blocked at many corporate networks however this issue is not there for OneDrive.