I'm currently using Thesis 1.8 and when you create a post there is a box underneath the editing section for you to enter the url of the 'post image'.
Thesis then displays that image as the main image of your blog post. It automatically crops it for the thumbnail as well.
When I've set up JM Twitter Cards with the summary card it's not using the image from the blog post. Instead it is defaulting to my Gravatar image as I've set that as a back up.
Is there any way I can get it to display the image from my post with out changing my current set up. Thesis handles the imaging for me.