19. The system of claim 17 , wherein descriptor points are feature vectors that define localized features of image content for a distinct book content item.
19. The system of claim 17 , wherein descriptor points are feature vectors that define localized features of image content for a distinct book content item. 20. The system of claim 19 , wherein the localized features comprise at least one feature selected from the group consisting of image colors, image edges and image intensity.