OverlappingElvis

If you’re sharing a link to a blog post on Facebook, having a thumbnail image makes for a much more effective share. If you have an image in the body of your post, Facebook will use that as the share image, but what if you don’t have any images in your post or want to specify an image you’re not using in the content? To solve this problem, I created a WordPress plugin that allows you to control which image shows when a link from your WordPress site is shared on Facebook.
<ul>
<li>Thanks to <a href="http://www.farinspace.com/wpalchemy-metabox/" rel="nofollow ugc">Dimas Begunoff</a> for the amazingly helpful <a href="http://www.farinspace.com/wpalchemy-metabox/" rel="nofollow ugc">WPAlchemy MetaBox PHP Class</a>.</li>
<li>I’m using the <code><link rel="image_src" href="…" /></code> approach. If you’re adding more Open Graph meta tags to your <code><head></code>, you’d probably want to use <code><meta property="og:image" content="…" /></code>, but in that case you probably also don’t need this plugin.</li>
<li>If you’re using any other plugins that add sharing info, Open Graph tags, or similar, this plugin will probably conflict with those.</li>
</ul>
For questions, comments, or bugs, you can reach me at <a href="http://twitter.com/Overlapping" rel="nofollow ugc">@Overlapping</a> or OverlappingElvis [at] gmail [dot] com.

Custom Image_Src

Specify a custom sharing image for Facebook. You can upload an image, use the first image in the post, or use the post thumbnail.

aitor.delapuente

This plugin helps ensure your content has a relevant thumbnail when shared on social sites.
Adds an image_src and og:image meta tags to your header using post thumbnnail (you must have post thumbnails / featured image enabled), first image on post/page content, or a defined default image.

FetenWeb image_src Metatag

This plugin helps ensure your content has a relevant thumbnail when shared on social sites.

Custom Image_Src vs FetenWeb image_src Metatag