If you host on your server, the path is predictable, it will be www.url.com/images/filename.jpg
If you host on webflow, just put your image on a dummy page, publish and right click on the image to copy the url. It could besimpler but it’s taking a minute, not hours.
In both cases your image needs to be attached to a style or put in a page to be sure it’s published and stays there when you duplicate or clean the site.
When I work with a client, I tell him to manage the open graph image by hislef by uploading a “opengraph.jpg” image at the root of his site, so I already know the url to put and I don’t depend on the client to state it. Then he can change it when he wants by swapping images on the server.