EXMAGE WordPress Image Links Plugin

Here is another plugin that lets you use external images as featured images on your website. EXMAGE lets you enter single or multiple images by entering their URLs in the backend. These images can be used like normal images but will have an icon to set them apart from regular attachments.

Just like regular images, your external images will have attachment IDs that you can use in your code. You can download this plugin for free at this time. More information is available here.