RSS Image Feed plugin by tepelstreel doesn’t create a feed of images, but ataches the first image of the post to your feeds. Normally only the content has images showing. With our plugin there will be a clickable image even in the excerpt and in the content there will be only one image instead of all the images of the post.
The author says the plugin was tested up to WP 3.1.
Download and info: http://wordpress.org/extend/plugins/rss-image-feed/