I provide a way that how i handle this problem, and the code is as follows
```
options = {
  ...,
  paste_preprocess: (editor, args) => {
    if (/^https?\:\/\/.+(png|jpg)$/.test(args.content)) {
      args.content = uploadByThirdPartyUrl(args.content);
    }
  }
}

```
[`paste_preprocess`](https://www.tiny.cloud/docs/tinymce/6/copy-and-paste/#paste_preprocess) allow us modify the pasted content before it gets inserted into the editor.
I judge if the pasted content is a third party URL; if true,  i will send it to the server and get a new URL to replace the original URL.

I don't know if my answer will help you, if not or has a better way, please let me know. Thanks:)