jmarreros

This Plugin allows to use an external image as Featured Image, this can be especially useful if you house your images in another location.
This Plugin is compatible with Nelio External Featured Image Metadata, so you can reuse your data in case you want to uninstall Nelio Plugin.

External URL Featured Image

It is what I was looking for: simplicity.

$external_image = get_post_meta( $post->ID, '_dcms_eufi_img', true );

Works well for me

Use an external url image as Featured Image for your posts, pages, and other kind of post types.

cubecolour

A simple and lightweight plugin to indicate external http and https links in posts, pages and custom content by appending a small diagonal arrow icon to the link.
No configuration is required just install and activate.

Indicate External Links

Very reliable has survived many Wp updates and just keeps working.

This plugin just keeps on working

Indicates external links in post, page and custom content.

External URL Featured Image vs Indicate External Links