This update of the plugin adds a neat feature which will attempt to find the first image in a post content and use this as the thumbnail for the summary even if no image was attached to the post itself (a common issue with WordPress and excerpts).
You can now also specify the dimensions of the image thumbnails using the options e.g:
force_image_height='150'
force_image_width='150'
See this post for details or visit the official WordPress plugin page for the download.
