When I try to share a "discussion" (which is merely a link from our website) at linkedin through the "Attach a link", it used to pull a nice image earlier, but it ceased to do so now.
Is there a meta property="og: we should specifically use for linkedin shares to have an image shown?
The LinkedIn share functionality supports a small subset of open graph tags as documented here: https://developer.linkedin.com/documents/setting-display-tags-shares
Note that at least until recently (and possibly still) re-scraping of existing shared pages is broken, so if you've already shared a page and it got the wrong image you're stuck unless you share it with a different URL.