RSS feed lacking images

Hi all,

As I understand it, a theme is responsible for how the RSS feed is generated [this comes from feed.press, my RSS service I've used since feedburner went away]. Even w/o them in the picture, I am noticing the RSS is lacking having the first image attached to my RSS feed for posts. The post type I am using is Image, and the posts [for now] are very simple - a photo of the day, with a short description of the photo below it as the post text. Clearly an RSS reader will wonder what the text is about if they don't also see the photo. :)

I've run another blog very similar to this which does include the photo in the RSS feed [the blog is offline now as I do major re-working to it, so I can't easily check how that one is working, but it is not using GP as its theme].

Can you point me to the documentation that may help me solve this issue? Thanks very much!