Writers are often told “write what you know.” For fiction writers this may mean writing about people you know. Most writers base their characters, at least in part, on people they have known. But they combine attributes, change identifying details, or otherwise disguise the descriptions so the people are no longer recognizable. Unless you want to risk legal problems, you should be very cautious when using real people in your writing.
Public figures (note the word “public”) have less expectation of privacy than the average person. Descriptions, and even photographs, of celebrities going about their lives are often are published without problems. They may complain, but unless the written account is known to be untrue, designed to cause harm, and damages the person’s reputation, lack of privacy is the price they pay for fame. That said, celebrities have deep pockets for attorney fees, and even if the lawsuit is baseless, you will spend a lot of money defending yourself.
We had two stories in recent Rehoboth Beach Reads books that featured public figures. One was a fictional account that involved Oprah Winfrey. It included several joking, but negative comments, and was obviously not based on anything she had ever actually done. The author was asked to change the name and disguise the details to avoid any possibility of a lawsuit. Another story featured an author’s experience seeing rock musician Dave Grohl in Rehoboth. The story was true and not disparaging in any way. That story was published using the celebrity’s name.
It’s a different situation when you drag your neighbor, ex-husband, or mother-in-law into a story. Even if what you describe is true, private individuals have a right to privacy. You should not use a real individual’s name, photo, or identifying information without permission. Even if the depiction is positive, you can get into trouble for using someone’s likeness, name, or identifying information for commercial purposes. This is true even if that person is dead.
Here is a good overview of how to use real people in your writing: http://helensedwick.com/how-to-use-real-people-in-your-writing/