Works created by the U.S. federal government, such as the passport cover design, are ineligible for copyright within the United States. If the passport design was created by the U.S. federal government (and not a third party who later transferred ownership to the government), then the passport design is in the U.S. public domain and may be photographed, copied, and modified freely. (Obviously, using the design to create a forged passport is illegal, but would not be a copyright offense.)
However, the U.S. federal government can assert copyright on their works in nations other than the United States:
Copyright laws differ internationally. While a U.S. government work is not protectable under U.S. copyright laws, the work may be protected under the copyright laws of other jurisdictions when used in these jurisdictions. The U.S. government may assert copyright outside of the United States for U.S. government works.
Strictly speaking, outside of the U.S., your use would need to satisfy your nation's fair use laws (if any exist) or you would need to seek permission from the U.S. government. In practice, I am not sure how litigious the U.S. federal government is about pursuing derivative works of the passport design outside the United States, and I couldn't find any policy documents about it.
In contrast, the U.K. government has issued a document detailing the Crown copyright on their passport design:
The UK Passport (the Passport) is subject to Crown copyright protection under section 163 of the Copyright, Designs and Patents Act 1988. This means that it may not lawfully be reproduced without the prior permission of the Controller of Her Majesty’s Stationery Office...
In particular, the documents says about the cover:
The image of the cover of the Passport including the Royal Arms, or the details pages of the Passport may not be used:
- as the main focus of the cover of a work, for example, the dust jacket or cover of a
- in advertising
- in facsimile form for use as a passport holder or cover
Wikipedia's image of the U.K. passport cover is labeled as a non-free image that is under Crown copyright. It is reproduced only under the belief that their encyclopedic use of the image satisfies U.S. fair use criteria.