add_action('rest_api_init', 'register_rest_images'); function register_rest_images() { register_rest_field(array('post'), 'fimg_url', array( 'get_callback' => 'get_rest_featured_image', 'update_callback' => null, 'schema' => null, ) ); } function get_rest_featured_image($object, $field_name, $request) { if ($object['featured_media']) { $img = wp_get_attachment_image_src($object['featured_media'], 'thumbnail'); if (empty($img)) { return false; } return $img[0]; } return false; }