In the case of same-day registration (notice--SAME DAY!!) a voter can be asked to present some form of photo ID. 2011 Iowa Law, Title II, Subtitle 1 "Elections", Chapter 48A, Section 7A, Paragraph 1, b1:
48A.7A Election day and in-person absentee registration.
1. a. A person who is eligible to register to vote and to vote may register on election day by appearing in person at the polling place for the precinct in which the individual resides and completing a voter registration application, making written oath, and providing proof of identity and residence.
b. (1) For purposes of this section, a person may establish identity and residence by presenting to the appropriate precinct election official a current and valid Iowa driver's license or Iowa nonoperator's identification card or by presenting any of the following current and valid forms of identification if such identification contains the person's photograph and a validity expiration date:
a) An out-of-state driver's license or nonoperator's identification card.
(b) A United States passport.
(c) A United States military identification card.
(d) An identification card issued by an employer.
(e) A student identification card issued by an Iowa high school or an Iowa postsecondary educational institution.
It goes on from there....but a registered voter does not need identification!!
Just so someone doesn't get too bent out of shape in case they overhear someone being asked for ID, it may not hurt to make sure of the circumstances before getting all uptight. But, there ain't NO WAY I'm presenting an ID!!!