Custom Preview Images For Trade Show Displays Blog

So, I’m SURE this is a nobrainer. But because It’s super late, I’m sleep deprived and i’m sure most other wordpress programmers are too… I’ll just ask:

How do I change the preview images in my trade show displays blog to AUTOMATICALLY show the first image in the post?

OR… for that matter, just not show the sushi stock images?

Thanks. I love the theme. It’s really clean.