How to change "Header" image look like "OpenCart"?

Hello,

I liked the "OpenCart" home page 'Header" image. Is it possible to change the default OpenCart Demo image to this style? I checked the CSS for OpenCart home page:

The size of the image: 900px × 5px and the size of the Demo image is: 1px 40px

So how I can replace this new image without distortion? Thanks in advance!