The Yale Art Gallery says it has the portrait, but does not know the artist and that the portrait is not currently on display at the gallery. However, it also says that the image is available for public use, but does not specify the exact Creative Commons license. See https://artgallery.yale.edu/using-images. However, I do not have time to to email the gallery myself.
The person who associated a work with this deed has dedicated the work to the public domain by waiving all of their rights to the work worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law. You can copy, modify, distribute and perform the work, even for commercial purposes, all without asking permission.
http://creativecommons.org/publicdomain/zero/1.0/deed.enCC0Creative Commons Zero, Public Domain Dedicationfalsefalse
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