[SOLVED] Creating a Fluid Image Header

I am creating a new site for a non-profit using ATO 3.5.3 wp.aauwatlanta.org We want to use an image banner for the header using stitched photo images. The image is 1200 pixels wide X 180 pixels high; the page width is set to fluid max. width 1280 pixels.

The problem is the page width is fluid but the image width is static. When zooming in the banner image is cut off. I tried ever combination of fixed or fluid width settings, but find none to resolve the behavior. Is it possible to set up the banner image to be fluid while maintaining the aspect ratio?

Thank you,

TerryEsh