Nirmal Kumar Ram

Magnigenie

WP Remote Thumbnail is a very lightweight WordPress plugin that comes with zero configuration and one-click setup. Using this plugin, you can easily set any external image as the featured image of any post/page or even custom post types.
This plugin automatically adds a custom metabox to each post type that supports post thumbnails. You just need to copy and paste the URL of any image into the metabox and click publish/update.
<iframe loading="lazy" class="youtube-player" width="750" height="422" src="https://www.youtube.com/embed/28J9IYZ4WFI?version=3&rel=1&showsearch=0&showinfo=1&iv_load_policy=1&fs=1&hl=en-US&autohide=2&wmode=transparent" allowfullscreen="true" style="border:0;" sandbox="allow-scripts allow-same-origin allow-popups allow-presentation allow-popups-to-escape-sandbox"></iframe>

WP Remote Thumbnail

A small lightweight plugin to set external/remote images as post thumbnail/featured image.

Mohamed Tawfik

This plugin let you add a featured image to a post using external URL.
You can use images from Flickr, google images… etc just in one click. 
No need to download the image and re-upload it again.
The image will be processed and thumbnails will be generated just like if you uploaded the image your self from your PC.
It is working with native and custom post types.
It is available now in two languages:
1- English 
2- Arabic
You can translate it to any languages.

WK URL 2 WP Thumb

This plugin let you add a featured image to a post using external URL.

WP Remote Thumbnail vs WK URL 2 WP Thumb