All Visa Waiver Program (VWP) emergency or temporary passports now must be electronic passports (e-Passports) to be eligible for travel to the U.S. without a visa. This includes VWP applicants who present emergency or temporary passports to transit the U.S. An e-Passport contains an integrated chip that stores biographic data, a digitized photograph, and other information about the bearer, and is distinguished by a gold-colored symbol on the passport’s front cover. VWP applicants arriving in the U.S. with a non-compliant passport may be required to undergo further processing and/or denied admission. U.S. Customs and Border Protection (CBP) may exercise discretion at the ports of entry in cases of medical or other emergency travel.
Source: CBP notice released July 14, 2009, contains additional country-by-country details.