variable/token_filter

http://www.drupalfoo.com/drupal-7-adding-custom-ui-maintainable-site-variables
token_filter
variable

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function condesan_variable_info() {
  $variables['condesan_logo_path'] = array(
    // 'name' isn't really necessary, as it will get populated from the key of this array above.
    'name' => 'logo',
    'title' => t('CONDESAN logo'),
    'type' => 'string',
    'description' => t('Print logo of CONDESAN'),
    'default' => base_path() . path_to_theme() . '/images/logo_condesan.jpg',
    'token' => TRUE,
  );
  return $variables;
}