Here is another Halloween postcard I've run across that takes inspiration from an Oz illustration. My blog entry for October 31st of 2008 featured a postcard that adapted a John R. Neill illustration for holiday use. This time an unidentified artist has been inspired by W. W. Denslow, rather than Neill.
The pose of the scarecrow is clearly based on Denslow's illustration of the Scarecrow being attacked by the Wicked Witch of the West's crows. Rather than copying the image precisely, the artist has made a number of changes to the scarecrow figure. However, the pose is too similar to be coincidental — also, the crow on the postcard is identical to the second crow above the Scarecrow's head in Denslow's drawing!
I found this image on the internet and don't currently own a copy of this card. It was manufactured by the Metropolitan News Company and dates from around 1907 - 1915.