This picture was chosen to represent Mercutio. He is the joker of the group and can never take things in a serious manner. Even on his death bed when he is stabbed by Tybalt he is still joking and saying oh it's only a scratch but he is also furious that he was caught in the two houses feud because he didn't belong to either if the families. He is also always teasing everyone about their problems such as Romeos love life but on the other hand he can go a little crazy at times.
The history of the joker playing card is the history of the fool or jester from the middle ages in Europe. But the role of the trickster is as common as the modern late-night talk show host, or the artists of comedy and parody in ancient Greece.