Code to block the wrong thumbnails?

Hello, this issue has been haunting me for some time. Basically, my blog gets a good deal of traffic rom Reddit.com but that site has a nasty habit of picking the wrong thumbnails for posts. There are no meta tags to force it to do the right thing, but I realized that it has been taking the first image available on the right sidebar.

I was wondering if it was possible to insert some code in a text box at te top of the sidebar that would force a redirect to the featured image, or otherwise link to it, so that when Reddit looks at the site it jumps away from the sidebar and to the images on the actual post.

Any ideas? Thanks.