Header Image That Scrolls With Wrapper

I Want to Add a header images that will scroll with my wrapper. My Theme uses the following code in the header.php to apply a theme option. I just want an image. Can anyone show me how to change it?

</div>
<div id="headerimg">
<?php if (is_front_page()) { ?>
     <h1><a>"><?php bloginfo('name'); ?></a></h1>

<?php } else { ?>
      <a>"><?php bloginfo('name'); ?></a>

<?php } ?></div>
<div class="description"><?php bloginfo('description'); ?></div>

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