Hi, Miriam!
This is more than what I had asked you to do (just Describe a picture); you have also given us a very interesting definition of what Art is! Thanks for sharing your ideas and good work!
Regards,
Marga

Miriam for me graffitis are a form of art, the last graffiti is of Banski, a grafittero of London with veryf prestigious in the world. Now we have got to distinguish a graffiti from an act of hooliganism, are paints in the street with aren´t art, are only acts of hooliganism.
But theer are true artistic graffitis such as the four you put in your post.
Greetings
Conchita

(fenquiu Florina pola traducción), :)