Sort images by creation date

I'm trying to understand the code. In node.module I found:

/**
 * Save a node object into the database.
 */
function node_save(&$node) {

[...]

  // Set some required fields:
  if (empty($node->created)) {
    $node->created = time();
  }

[...]

  $node_table_values = array('nid' => $node->nid, 'vid' => $node->vid,
                    'title' => $node->title, 'type' => $node->type, 'uid' => $node->uid,
                    'status' => $node->status, 'created' => $node->created,
                    'changed' => $node->changed, 'comment' => $node->comment,
                    'promote' => $node->promote, 'sticky' => $node->sticky);
  $node_table_types = array('nid' => '%d', 'vid' => '%d',
                    'title' => "'%s'", 'type' => "'%s'", 'uid' => '%d',
                    'status' => '%d', 'created' => '%d',
                    'changed' => '%d', 'comment' => '%d',
                    'promote' => '%d', 'sticky' => '%d');

  //Generate the node table query and the
  //the node_revisions table query
  if ($node->is_new) {
    $node_query = 'INSERT INTO {node} ('. implode(', ', array_keys($node_table_types)) .') VALUES ('. implode(', ', $node_table_types) .')';

[...]
  }

  // Insert the node into the database:
  db_query($node_query, $node_table_values);

[...]

}

This is the right place to start, isn't it? But I don't want to change its behaviour for all node types, only for image nodes. So I have to override something, right? But what to override? And where? Is this what hooks are for?

Do I need something like this:
http://api.drupal.org/api/file/developer/hooks/node.php/6

After inserting this into the image.module function "image_submit" the exif date is being used as the node's creation date.

function image_submit(&$node) {
  // --- EXIF ---	
  $file = file_create_path($node->images['_original']);
  $exif = exif_read_data($file, 0, true);
  $exif_date = $exif['EXIF']['DateTimeOriginal'];
  $node->created = strtotime($exif_date);
  // --------------
  if ($node->new_file) {
    $node->rebuild_images = FALSE;
  }
}

Unfortunately gallery still displays the images in the wrong order...