murraypicton

<p>Uses the flickr API to select a random image for a specified user.  This image is then displayed at the beginning of every blog post and saved so that each post always has the same image.</p>
<h3>Copyright Notice</h3>
<p>Ensure you have the permission to use the flickr user’s photos before using this plugin.  The writer of this plugin takes no responsibility for misuse and copyright disagreements.</p>


flickrImg

Put a random flickr image for a specified user as the main image for each post

jmarreros

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


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.

flickrImg vs External URL Featured Image