First, the photo is a mechanical scan/photocopy of the original cover and does not qualify for independent copyright protection.
Second, the dust jacket was first published prior to 1978 without a valid copyright notice. The hardcover book itself carried a copyright notice, so its contents remain copyrighted. However, the first-edition dust jacket did not carry a separate copyright notice. 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."
The jacket's lack of a copyright notice is self-verifying; someone looking to double-check can examine the entire image.
Keep in mind that the pre-1989 requirements for copyright notice were highly formalistic and, other than a few enumerated exceptions, required these three elements:
This image is in the public domain because it is a mere mechanical scan or photocopy of a public domain original, or – from the available evidence – is so similar to such a scan or photocopy that no copyright protection can be expected to arise. The original itself is in the public domain for the following reason:
Note that it may still be copyrighted in jurisdictions that do not apply the rule of the shorter term for US works (depending on the date of the author's death), such as Canada (50 p.m.a.), Mainland China (50 p.m.a., not Hong Kong or Macao), Germany (70 p.m.a.), Mexico (100 p.m.a.), Switzerland (70 p.m.a.), and other countries with individual treaties.
This tag is designed for use where there may be a need to assert that any enhancements (eg brightness, contrast, colour-matching, sharpening) are in themselves insufficiently creative to generate a new copyright. It can be used where it is unknown whether any enhancements have been made, as well as when the enhancements are clear but insufficient. For known raw unenhanced scans you can use an appropriate {{PD-old}} tag instead. For usage, see Commons:When to use the PD-scan tag.
Note: This tag applies to scans and photocopies only. For photographs of public domain originals taken from afar, {{PD-Art}} may be applicable. See Commons:When to use the PD-Art tag.
Captions
Dashiell Hammett, US writer of hard-boiled detective fiction
== {{int:filedesc}} == {{Information |Description={{en|1=Photo portrait of American author Dashiell Hammett used for the first-edition dust jacket of his fifth and final novel, ''The Thin Man''.}} |Source={{en|1=High-res scan via [https://twitter.com/ManuB72179071/status/1133093347890028544 Twitter]. Cropped at a 5:4 ratio toward his head and upper body, retaining the dramatic shadow cast on the wall.}} |Date=1934 |Author={{en|1=Photographer unattribu...