Do you think it's normal for a grown man to have a book filled with pictures of naked little boys, in various poses?
Define normal. This may shock you but not everyone sees the naked human form as inherently sexual. Without having seen the pictures I won't make a judgement as to their artistic or aesthetic values nor can I judge whether or not Jackson saw them as sexual. Many people have collections of artistic photographs which may depict nudity in some tasteful manner. While pedophiles might enjoy such a book, not everyone who enjoys such a book is necessarily a pedophile.