Same trick painted in 1670!
http://www.futilitycloset.com/2012/05/16/reverse-psychology/ 

Possible reference to Cornelius Norbertus Gijsbrechts – Trompe l’oeil. The Reverse of a Framed Painting, 1670
http://www.smk.dk/en/explore-the-art/the-royal-collections/european-art-1300-1800/highlights/cornelius-norbertus-gijsbrechts-trompe-loeil-the-reverse-of-a-framed-painting/

Should say “this is not the back of a painting” on the Magritte