Four people who have never been in my kitchen (the second)

What do these four people have in common?

• Marian Anderson
• Bob Dylan
• Ezra Pound
• Donald Rumsfeld

Answer (unless it's left in the comment box) after I get back from lessons tomorrow evening... 8:30-ish.

Previous entry in the series here.

UPDATE 2/7: The answer? They all were subjects of Richard Avedon portraits. (Names now link to the picture)