This very done video covers changing the header image in WordPress. The tutorial uses the default 2012 Theme which still is included with any new WordPress installation. The video covers all aspects of working with WordPress headers.
You learn how to change the header, or how to remove it entirely if you choose. Customizing the header image allows you to personalize your site to let visitors see right away what the site is about.
Philip Glenhill published the video on http://pressuser.com originally. The video covers the important ppoints well, giving you the information you need without wasting your time.