The Yoast WordPress-SEO is a great plugin for getting SEO on your blog in an easy to use, and easy to manage function.
Recently I encountered an issue where the <meta> og:image links were not being served over our CDN, and were referencing their original image locations. og:image meta tags are used by Facebook and Twitter to give users the various thumbnail options when they create a post in Facebook that includes the link to a site/page/post.