I solved my problem in Cpanel, "Security" section > "Hotlink protection" where I turned on the option "Allow direct requests (i.e., entering the URL of an image into a browser"
However, you have a completely different problem and it probably lies in your FB Social Reader plugin or the open graph meta data.
In my case, the thumbs didn't load, I was getting an empty square, cause FB couldnt retrieve the image from my site due to my hotlink settings. FB was like "give me the image, I'd like to show it" and my Hotlink protection said "no, you can't have it".
Your case is different. There IS a thumbnail, but a wrong one, here it is: http://www.thesteadytable.com/wp-content/plugins/fb-social-reader/images/fbdefaultarticle.png
It is a default image from your FB Social Reader plugin. If you can open the plugin's settings in your WP Dashboard, try to see if you can specify a different image.
FB cannot "see" the right thumbnails from your site and retrieves the default one provided by your plugin. It's like FB says: "give me thumbs", the plugin says: "ok, but you can have only this one"
This happens only with your individual posts. If I post a link to your homepage: http://www.thesteadytable.com on my FB, the thumbs appear without problems and I can even choose.
There are also other issues with your site.
I checked it with the fb debug tool: http://developers.facebook.com/tools/debug
I got the following warnings in FB debug tool for your homepage:
Open Graph Warnings That Should Be Fixed
Inferred Property: The 'og:url' property should be explicitly provided, even if a value can be inferred from other tags.
Inferred Property: The 'og:description' property should be explicitly provided, even if a value can be inferred from other tags.
Inferred Property: The 'og:image' property should be explicitly provided, even if a value can be inferred from other tags.
And I got this warning in fb debug tool for individual post:Parser Mismatched Metadata:
The parser's result for this metadata did not match the input metadata. Likely, this was caused by the data being ordered in an unexpected way, multiple values being given for a property only expecting a single value, or property values for a given property being mismatched. Here are the input properties that were not seen in the parsed result: 'og:title'
This is the line that specifies an image for individual post:
Meta Tag: <meta property="og:image" content="http://www.thesteadytable.com/wp-content/plugins/fb-social-reader/images/fbdefaultarticle.png" />
I never used that plugin, but i guess that you can open its settings and specify another image, so the meta property og:image will show url to it. Speaking of other issues reported by the debug tool, I'm not sure how to solve them, perhaps you should check your plugin or try to put everything in order manualy in your header file.