Word processors may put markup fragments that reference locally saved image files/embedded objects on the clipboard. Ideally, these files should be exposed in the DataTransferItemList so that scripts can process them and upload them to the backend on paste.

Now, obviously we don't want any random page to be able to write <img src="file:// ..."> to the clipboard, then trigger paste and steal the referenced local file. Ideally, the implementations should be able to deduce that the content is from a local application to be able to do this safely. I don't know if that is possible, certainly not if it's possible cross-platform.