We'll create fresh WordPress site with OGP Generator installed. You have 20 minutes to test the plugin after that site we'll be deleted.
When shared on Facebook, this plugin shows a nice Thumbnail of your posts, pages and site.
<meta property="fb:app_id" content="you can specify in admin" />
<meta property="og:title" content="Post Title" />
<meta property="og:type" content="article" />
<meta property="og:url" content="Post URL" />
<meta property="og:image" content="Post thumbnail, attached image, the first image or default image which you upload" />
<meta property="og:site_name" content="Site Title" />
<meta property="og:locale" content="Your Locale" />
<meta property="og:description" content="Post excerpt or text generated from your content" />
When home page, archive pages, search result page or what ever else pages are shared on facebook, og:image will be the image you specify in Settings > Reading > OGP Settings.