I scanned the internet for an hour; reverse image searching with every engine to find any sign of a copyright notice, as well as checking for potential copyright renewals. Out of the dozens of sites using the image, none of them I found even provided adequate attribution; leaving me to believe that this image's copyright expired without a notice, especially considering the time period that Duke served as the Grand Wizard.
This work is in the public domain in the United States because it was published in the United States between 1929 and 1977, inclusive, without a copyright notice. For further explanation, see Commons:Hirtle chart as well as a detailed definition of "publication" for public art. 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.