The little blue book that opens doors around the world is about to get a big technological face-lift.

Beginning next year, new U.S. passports will contain a computer chip embedded in the back cover that will store all of the document's printed biographic information plus a digital photograph that authorities say is harder to alter.

The microchip, which won't be noticeable, can be waved in front of a reader without contact -- similar to the E-ZPass system -- and will contain enough room to ultimately hold multiple photos or other identifying marks, said Kelly Shannon, spokeswoman for the Bureau of Consular Affairs.

The switch to a computer chip aims to address security concerns raised in the wake of 9/11, Shannon said. Although travelers will not be required to replace existing passports, any renewed or new passports issued by mid-2005 will contain the microchip.

The same applies to foreign travelers entering the United States: After September 2005, new passports issued to residents of non-visa countries, such as France or Spain, must contain a chip.

"With the old passport, someone could physically cut into the passport photo," Shannon said. "It's going to make it much more difficult to tamper with. What we're really looking to do is verify more thoroughly who is traveling."

As with any technological innovation, the new passports will only be as good as those who monitor them, said Daniel Solove, a professor at George Washington University Law School and author of "The Digital Person: Technology and Privacy in the Information Age."

Whether a thief can use someone else's chip will depend on how many points of identification screeners will require at points of entry and departure, Solove said.

Moreover, if a document that stores a fingerprint or retina scan is lost or stolen, the identifying mark can be replaced, but Solove said the process will take time.

The changes have been met with resistance from civil rights advocates and legal experts who say the technology brings the country one step closer to a Big Brother future.

Although federal officials stress that the chip will contain the same information currently printed on a passport, members of the American Civil Liberties Union say they are primarily worried about the non-contact nature of the chip, which raises the possibility that the contents could be read surreptitiously.