How to successfully implement og:image for the LinkedIn

This answer I found on LinkedIn forums might be of help to you:

Guys, I’ve spent a whole day trying different things. What worked for
me is using the mata [sic] tags as following:

<meta prefix="og: http://ogp.me/ns#" property="og:title" content="{Your content}" />
<meta prefix="og: http://ogp.me/ns#" property="og:type" content="{Your content}" />
<meta prefix="og: http://ogp.me/ns#" property="og:image" content="{Your content}" />
<meta prefix="og: http://ogp.me/ns#" property="og:url" content="{Your content}" />

Just try to add prefix to every tag (not to html tag), then re-sign in
with your LI account to clear the cache…
Post your results.