Whenever I create a new WordPress theme, I like to make image management as easy as possible for the end user, including myself on my niche sites. Here’s what I use that enables me to upload a single image to the WordPress media library, and automatically display web optimized versions in different sizes throughout my theme.
Mathew Ruddy has a great addon for WordPress that does just this. It is an image resizing function that provides WordPress users with an alternative to Timthumb, which is another popular image resizing function but has been know to have some security issues. Now that WordPress has image resizing and cropping built right in, we can utilize that native resizing functionality and mimick the Timthumb resizing functionality.