Yes, I wrote a guide here about how to do it, and a template to make it easier and cleaner.

Or they can put the images on a template here and transclude it to the other wikis.

So, to be clear, it isn't external in the sense that it is stored on some other website. However, it is external in the sense that it won't show in the wiki's list of files.

I also suspect that if you cancel the post, the image may be deleted in some cleanup process in the future.

It might be, but I have never seen that happen.

@Caburum Not a bad guide, but you might want to specify that you need to be in a desktop browser (you should say which one you used for your examples). Also, since it uses Community Central, I'm not sure how reliably you can predict if the images will stay around. FANDOM may clean up images from time to time.

I was hoping for something like when you choose to paste an image via "copy image location" into places like Twitter, Discord and FaceBook, it shows the the image along with the link, no uploading the image required.

That is not possible on Fandom for external images, only for images stored on their server, so they must upload it this way or another.

There are many good reasons (to FANDOM) not to allow external images not on their servers to be rendered and have links.

@Fandyllic that makes sense.