Marcel Duchamp's L. H. O. O. Q. was a postcard that he got from The Louvre and painted facial hair on what was thought to be the most remarkable piece of art at the time. The title, phonetically turns out to mean, "She has a hot ass." Which is iromic because the viewer can't see past her upper body in this painting or on the postcard. He was trying to tell the artists of this age that they are taking themselves all too seriously and needed to lighten up. I don't know that that was the message that they got from this, but that was what Duchamp was trying to get across.
This Mona Lisa picture was made by Andy Warhol many years after Duchamp's postcard was made. Although I don't think this depiction of the Mona Lisa was meant to serve as a wake up call to other artists as Duchamp's was, this picture of Mona Lisa was made by taking a photogenic silkscreen of Mona Lisa, and using gold on white instead of the usual underpainting of the canvas to make this picture look as if the viewer were looking at a picture done in photographic negatives. This was meant to give Mona Lisa an angelic quality about her.
There is a song called, "The Ballad of Mona Lisa" by Panic! At the Disco. Some of the lyrics say that Mona Lisa is guarenteed to run this town tonight. And this is how the original painting of Mona Lisa was. It was considered the most magnificent painting of the time made by anyone. Nothing was able to compare to it and nothing was as good as it was. The song refers to, whether it be directly or indirectly, the ultimatum that this painting had put on the art in this period of time.
Thus, this painting is still having influence to this day on things that we hear and see every day.