International Copyright and Trademark laws protect all of the artwork of M.C. Escher. Any reproduction of his work, including downloading, is prohibited without the express written permission of the copyright holder.

Contact regarding all matters pertaining to reproducing Escher's artwork and writings.

Here is a more extensive commentary from Wikipedia:

Ownership of the Escher intellectual property and of his unique art works have been separated from each other.
In 1969, Escher's business advisor, the late Jan W. Vermeulen, author of a biography in Dutch on the artist, established the M.C. Escher Stichting (M.C. Escher Foundation), and transferred into this entity virtually all of Escher's unique work as well as hundreds of his original prints. These works were lent by the Foundation to the Hague Museum. Upon Escher's death, his three sons dissolved the Foundation, and they became partners in the ownership of the art works. In 1980, this holding was sold to an American art dealer and the Hague Museum. The Museum obtained all of the documentation and the smaller portion of the art works.
The copyrights remained the possession of the three sons - who later sold them to Cordon Art, a Dutch company. Control of the copyrights was subsequently transferred to The M.C. Escher Company B.V. of Baarn, Netherlands, which licenses use of the copyrights on all of Escher's art and on his spoken and written text, and also controls the trademarks. Filing of the trademark "M.C. Escher" in the United States was opposed, but the Dutch company prevailed in the courts on the grounds that an artist or his heirs have a right to trademark his name.
A related entity, the M.C. Escher Foundation of Baarn, promotes Escher's work by organizing exhibitions, publishing books and producing films about his life and work.