Hatch theme description: http://theme.wordpress.com/themes/hatch/
Hatch’s grid-style design relies heavily on featured images, so it looks its best when you assign one to each of your posts. You can do this using the Featured Image meta box when you create or edit a post.
Featured images will appear both on the blog as a preview and full size in single post view. Please note, on single posts the featured image will be duplicated if also included in the post content.
If no featured image is assigned, Hatch will attempt to pull the first attached image in your post. If no image is attached, the theme displays a light gray placeholder.