Copyright status of The Wizard of Oz and related works in the United States
"The Wonderful Wizard of Oz" was published in 1900, and was the first to enter the public domain in "1956". This allowed Reilly & Lee, the publisher of all the other Oz books (as well as Baum's other books) to issue their own edition of "The Wizard of Oz", which had previously been published by George M. Hill Company and later by the Bobbs Merill Company after Hill went bankrupt..
The Wonderful Wizard of Oz
A new edition of the book appeared in 1944, with illustrations by Evelyn Copelman. Although it was claimed that the new illustrations were based on Denslow's originals, they more closely resemble the characters as seen in the famous 1939 film version of Baum's book.