Paul O pointed me towards using media queries to target webpages for mobile devices.

In the examples in How To Use CSS3 Media Queries To Create a Mobile Version of Your Website - Smashing Magazine the images are displayed using background-image.

If I have a webpage with a banner at the top which is a JPG and then two <div> side by side in the middle where one of the <div> contains another JPG and then a footer, is my only option to create a separate page?