Make any inline image a featured image

If I understand this correctly, the featured image will be used to generate the thumbnail for the link to the post. Our posts will have various images inline with the article, we don’t really want a “Featured Image” highlighted at the top of the post. Is there a way to mark one of the images from within the post as the featured image? I’ll keep searching for an answer but have had no luck yet. Thanks for any input.

Twenty Twelve