old_contents: from django.db import models
  
  class Book(models.Model):
      """This model contains the information about the book owned by the owner
      such as book condition, etc.
      """
      book_generic = models.ForeignKey('catalog.BookGeneric')
      owner = models.ForeignKey('auth.User')
  
      def __str__(self):
          return "%s owns %s" % (self.owner, self.book)
  
  class BookPicture(models.Model):
      book = models.ForeignKey('ownership.Book')
      image = models.ImageField()
      created_at = models.DateTimeField(auto_now_add=True)
      modified_at = models.DateTimeField(auto_now=True)
  
new_contents: from django.db import models
  
  class Book(models.Model):
      """This model contains the information about the book owned by the owner
      such as book condition, etc.
      """
      book_generic = models.ForeignKey('catalog.BookGeneric')
      owner = models.ForeignKey('auth.User')
  
      def __str__(self):
          return "%s owns %s" % (self.owner, self.book_generic)
  
  class BookPicture(models.Model):
      book = models.ForeignKey('ownership.Book')
      image = models.ImageField()
      created_at = models.DateTimeField(auto_now_add=True)
      modified_at = models.DateTimeField(auto_now=True)
  
subject: Fix book reference