Having to download images somebody else uploaded for characters or items, only to then have to reupload them to this site when making new entries is tedious. Allowing for a box to enter the url of an image already online as an alternative to uploading your own images would speed up making multiple entries or updating visual changes of a character much faster and easier.
Comment from Team Critical Notes
This has been added for content images, but not yet for campaign backgrounds or avatars. This is still on the to do list.