I first saw this cover on the excellent picture blog, The Sweetest Psychopath, and I went digging for information. Turns out this is a French-language pocketbook published by Le Scribe of Brussels in 1946.
Note the author’s name, given as Ann Mary Shelley. The confusion persists on the book’s title page, where Mary is identified as May W. Shelley. The translator’s name is given as Henry Langon, assuming they got that one right. The cover artist escapes misidentification, he is not credited.
The fine, stark, two-color illustration is well composed, with a stonework arch mirroring The Monster’s curved back. As often happens, the iconography is inspired by movie themes instead of the book’s actual content, here with stormy skies, a castle in silhouette behind the title, and The Monster with neck bolts and a box head with forehead scar.