Create a WP plugin/code to automatically add upload source to imported image caption

We need a plugin or code snippet to implement in our wordpress child theme that does the following: When images are imported in a post from a url using the "add media" button in the post editor, we want the caption field for that image to be automatically populated with this: <a href="[imported image's source url"]>Source: [imported image's source (sub)domain</a> That's all. Thanks in advance for your bid.