If you've built a site before using the default Twenty Eleven theme, you may have used its featured image functionality.

Featured images are images which you add to a page or post outside the content of the post or page itself, as opposed to an image, which you would add into the flow of the content. WordPress can then display your featured images however you want, for example on an archive page it can display a small version of the featured image for each post above or next to its excerpt.

Featured images were introduced with WordPress Version 2.9, before that many developers created a special custom field, but it wasn't an ideal workaround. Featured images are a feature of WordPress that make theme builders and site owners' lives easier.

So let's add them to our theme.