When writing a biography about a celebrity or well known figure it is highly likely that there will be articles, extracts from other books, photographs and interviews that the writer wants to include in their book.
The way to get permission for use is to contact the copyright owner. They will sometimes want a fee for use but not always. The quickest way to start this search is by contacting the publisher of the source.
When writing to ask for permission to use then emails are acceptable but they should also be backed up by sending a paper letter aswell. The information which should be included when asking for permission is:
Not everything will need a permission for use but if hoping to better safe than sorry.