Drawings are OK, but photos are better. If you have a story about a photo which shows a ghost, don't you dare write about it unless you print the photo. I always send contrbutors a copy of the finished story before the book is printed. If something is factually incorrect, you have a chance to correct it. I do not ask for contributors' approval of the story or the way I portrayed them, just whether the facts are right.
People often have second thoughts when they see their stories down in black and white.
You will have to decide how you will handle this issue. I suggest taping all interviews with contributors so there are no misunderstandings. If you are truly paranoid, make contributors sign a release saying they will not sue you. Or run your manuscript by a lawyer to see if it contains anything libelous. Never promise a contributor that their story will appear in their book.