A work of the United States government, as defined by United States copyright law, is "a work prepared by an officer or employee of the U.S. government as part of that person's official duties." The term only applies to the work of the federal government, not state or local governments. In general, under section 105 of the Copyright Act, such works are not entitled to domestic copyright protection under U.S. law, sometimes referred to as "noncopyright." As an exception to section 105, 15 U.S.C. § 290e authorizes U.S. Secretary of Commerce to secure copyright for works produced by the Department of Commerce under the Standard Reference Data Act.
There's no need to "watermark" these photos. But if you must, can you please put the URL address, down at the bottom, in smaller font next time?
Ambassador Hume in Tank with Sharks