Some people save the image to their PC, and then upload it.
You know that's what they did if you quote the post with the image, and all you see are the quote commands with their names.
I'm too lazy to do that.
I just copy/past the URL from wherever I found it online into the VN image function.
So it might look like this:
[ img]https://dailylolpics.com/wp-content/uploads/2017/09/Halloween-soon.jpg[/img]
--except that I inserted a space after the very first [ . If you take out that space, post it in a reply, and hit preview post, you would see the image.
I don't know the trick (if any) if you are uploading from your PC, sorry.
--or do as Cookie advised, lol