Excerpt Images

Hi Tom,
Love this theme! Thank you very much.
One problem: I can't figure out how to add an image when I use excerpts.The only way I can get it to work is if I add a feature image. But I don't want to do that because when you click on the post I see the featured image at the top and the same image in the post. I don't want the double images. Is there a way to have your post image automatically show as the excerpt image without adding a feature image?
Hope this makes sense.
Thank you!
Barb