The full quote from Marcel Duchamp is given below:
The creative act is not performed by the artist alone; the spectator brings the work in contact with the external world by deciphering and interpreting its inner qualifications and thus adds his contribution to the creative act.
There is something important in what Duchamp said, something I must understand more clearly. He’s an interesting guy, take a look at what the Wikipedia article says about him:
- While he is most often associated with the Dada and Surrealism movements, his participation in Surrealism was largely behind the scenes, and after being involved in New York Dada, he barely participated in Paris Dada.
- Thousands of books and articles attempt to interpret Duchamp’s work and philosophy, but in interviews and his writing Duchamp only added to the mystery. The interpretations interested him as creations of their own, and as reflections of the interpreter.
- A playful man, Duchamp prodded thought about artistic processes and art marketing, not so much with words, but with actions such as dubbing a urinal art and naming it Fountain, and by “giving up” art to play chess. He produced relatively few artworks, as he quickly moved through the avant-garde rhythms of his time.
If he were alive today he’d probably be called something like RageBoy 
As far as I can make out, nobody sued Duchamp for doing this to the Mona Lisa:
In keeping with that, I have no hesitation in sharing what RageBoy did to the Scoble/Israel book. Do be careful, people have been known to injure themselves looking at this.
For those who are interested, it is worth reading Duchamp’s 1957 essay on The Creative Act. Thank you mindwebart3, whoever or whatever you may be, for the link.