As I understand it, in the United States police can only confiscate cameras/film/memory cards if -
(1.) they have a court order
(2.) they arrest you and your camera/film/memory cards are taken into evidence
Also -police may (or may not) be able to confiscate your film/memory cards if a crime has been committed and you have photographs that may be used as evidence. To the best of my knowledge, this would require a court order; they can't confiscate your property just because they are "the police."
Take a look at the following pages for clarification: http://www.krages.com/phoright.htm