Choose a default image that previews when sharing on Facebook

We publish image heavy posts. When our readers share our posts across Facebook, Facebook picks up any one of dozens of images from a post to preview with our links, images which are often confusing, out of context or don’t compel a reader to click (e.g. a screenshot that is text heavy, not a photo). How could write.as implement a way for us to select the default image the link is shared/previewed with, on social media?

Right now Write.as automatically chooses the first one in the post by default, and offers the first few as options on platforms that support it (like Facebook). One way to choose the default is to just put it before other images in the post. But maybe we could come up with another way to do this.