1. First, this digitally restored image derives from a scan of the original cover and does not qualify for independent copyright protection.
2. Second, the dust jacket was first published prior to 1978 without a valid copyright notice:

Gentlemen Prefer Blondes was first published in book form in 1925 by Boni & Liveright and presumably carried a copyright notice. However, this 1926 dust jacket by Grosset & Dunlap did not carry a separate copyright notice on the jacket whatsoever. (You can verify this information by inspecting the full jacket here.) According to The Compendium of U.S. Copyright Office Practices: Chapter 2200, § 2207.1(C) at p. 15:

"A notice of copyright on the dust jacket of a book is not an acceptable notice for the book, because the dust jacket is not permanently attached to the book. Likewise, a notice appearing in a book is not an acceptable notice for the dust jacket or any material appearing on that dust jacket, even if the book refers to the jacket or material appearing on the jacket."

Pre-1989 requirements for copyright notice were highly formalistic and, other than a few enumerated exceptions, required these three elements:

1. "The symbol © or the word 'Copyright' or the abbreviation 'Copr.' or an acceptable variant such as "(c)";
2. "The year of first publication for the work"; and
3. "The name of the copyright owner, or an abbreviation by which the name can be recognized, or a generally known alternative designation of the owner."

If just one of these elements is omitted, the work is deemed to be published without notice and is not eligible for copyright protection.