<?php if ( !function_exists('dynamic_sidebar') || !dynamic_sidebar("Sidebar") ) : ?>

<h6><?php _e('Pages','integramotion'); ?></h6>
      <fieldset>
         <ul>
            <?php wp_list_pages('title_li='); ?>
         </ul>
      </fieldset><hr />

<h6><?php _e('Categories','integramotion'); ?></h6>
      <fieldset>
         <ul>
            <?php wp_list_categories('title_li='); ?>
         </ul>
      </fieldset><hr />

......

<h6 class="some_class"><?php _e('Categories','integramotion'); ?></h6>
      <fieldset>
         <ul>
            <?php wp_list_categories('title_li='); ?>
         </ul>
      </fieldset><hr />

.some_class {
 background: transparent url('..... ./my-header-image.png') center top no-repeat;
}