Create a header as needed and once you have it on your site find out the pixel size.

Create as many header pictures as you want to use, my example was for pictures 974 by 225 pixels.

up load these pictures to your theme, my eample was to themes/arcus/images

Edit the style.css file

Find the section called div.art-header-jpeg

Change

  background-image: url('images/header.jpg');
  background-repeat: no-repeat;
  background-position: center center;

to

/*  background-image: url('images/header.jpg');*/
/*  background-repeat: no-repeat;*/
/*  background-position: center center;*/

In the Theme Directory

In your Theme

Edit header.php

change

to

My example is for a random number between 1 and 3 as I had three header(x).jpg files