
Traveling to San Francisco: What is Entry under Visa Waiver Program
A number of countries have Visa Waiver Agreement with United States. So citizens from those countries who have a Visa Waiver Program with the US may enter San Francisco without Visa but they are eligible to stay only for the duration of 90 days. For this these citizens must possess a machine readable passport which must contain a bar code on the photo page. From 26 October it has become mandatory that the eligible travelers under this scheme must posses a passport containing biometrics details.
http://blogs.siliconindia.com/ManishKumarJaiswal/Getting_USA_VISA__Rules_Documents_and_Tips-bid-vMbwDt0F57735294.html

