http://www.ramonfincken.com/permalink/topic211.html

1)
Install Custom Field Template ( wp-admin > plugins > add new )

2)
Config Custom Field Template like this ( Leave the rest as it is )

Template #0
* Template Title:
Header image

* Post type:
Both

* Template Content:
[File Upload]
type = file


3)
Make sure that in Atahualpa > Configure Header Area this is entered:
%image

4)
Now for 2 copy and paste actions in the code, use notepad/gedit/araneae whatever text editor you want.

OPEN
wp-content/themes/atahualpa/functions/bfa_header_config.php

DIY
Now make a backup of this file!

FIND
# Around line 274
// Header Image
if ( strpos($header_items,'%image') !== FALSE ) {

AFTER, ADD

   // Ramon Fincken, http://www.ramonfincken.com/permalink/topic211.html
   global $wpdb; // We need a DB object/connection

   $temp = get_post_meta($post->ID, 'File Upload', true);
   $sql = "SELECT meta_value FROM $wpdb->postmeta WHERE post_id = '".$temp."' AND meta_key = '_wp_attached_file'";

   $temp = $wpdb->get_results($sql, ARRAY_N);
   if(count($temp) == 1) // If we find an image
   {
      $temp_image = $temp[0][0];
      if(!file_exists('./wp-content/uploads/'.$temp_image)) // Make sure it _really_ exists on the server
      {
         unset($temp_image);
      }
   }
   // Ramon Fincken, http://www.ramonfincken.com/permalink/topic211.html


FIND
# Around line 300, partial find
$header_image .= ($bfa_ata['header_image_clickable'] == "Yes" ? '<div class="clickable">

BEFORE, ADD

   // Ramon Fincken, http://www.ramonfincken.com/permalink/topic211.html
   // File exists
   if(isset($temp_image))
   {
      $header_image = '<div id="imagecontainer" class="header-image-container" style="background: url(';
      $header_image .= get_option('home').'/wp-content/uploads/'.$temp_image; // GOGOGO !
      $header_image .= ') ' . $bfa_ata['headerimage_alignment'] . ' no-repeat;">';
   }
   // Ramon Fincken, http://www.ramonfincken.com/permalink/topic211.html




5)
Now go to a page or post and upload a new header image for that page !

You can always remove the image again and the default header image will be shown!