Limit Teaser to display only the first value of a Field
Create a custom module, replace MODULENAME with the name of the module and field_image with the name of your field:

/**
 * Implements hook_entity_view().
 */
function MODULENAME_entity_view($entity, $type, $view_mode, $langcode) {
  if ($view_mode == 'teaser') {
    $entity-&gt;content['field_image']['#items'] = array_slice($entity-&gt;content['field_image']['#items'], 0, 1);
  }
}


See the hook_entity_view() documentation for more details.