It is an intuitive sense, an ability that comes from a lot of practice. A photograph is a secret about a secret. The more it tells you the less you know. Not everybody trusts paintings but people believe photographs. You don't take a photograph, you make it.
Terrorists are tourists with guns.
Imagination gives you the picture. Vision gives you the impulse to make the picture your own. The happiest people are those who think the most interesting thoughts. Those who decide to use leisure as a means of mental development, who love good music, good books, good pictures, good company, good conversation, are the happiest people in the world. One ought, every day at least, to hear a little song, read a good poem, see a fine picture and, if possible, speak a few reasonable words.