Elements such as traditions, dominant styles, of popular forms that are common to several different types of art are called

This could be something like art conventions. So while you might have art from several different areas, they use similar techniques because these represent the conventions of the art itself. For example, you could have artists from two different countries in Europe that speak different languages, etc but they both use the same conventions of the impressionist style because that's inherent in the particular style of art.

Photojournalism adds emphasis and power. if some one told you that a bomb blew up the world trade center, you wouldn’t have believed them until you saw it on the tv or in the newspaper.