Image width determined by screen width?

Hello,

I am trying to use a jpeg image as a banner or stripe at the top of an html page. I do not want this stripe to be so wide that a user can scroll over, I want it to be just as wide as the viewable area of the screen. So, the image needs to resize to match the width of the user’s screen.

What is the best way to do this?

Thanks for the help.