Wis. Stat. § 814.11: Disbursements, how proved.

Charges in a bill of costs for witness fees, or copies of documents or other disbursements, except to officers for services shall not be taxed without an affidavit stating the distance the witnesses respectively traveled and the days they actually attended, and an affidavit that such copies were necessarily obtained for use; nor shall such other disbursements be allowed without an affidavit specifying the items thereof, nor unless they appear to have been necessary and reasonable in amount.