How did the sixty-four hexagrams and images in the Book of Changes come from?

The preface of the sixty-four hexagrams in the Book of Changes is based on eight diagrams. The predecessors' main understandings are "innate gossip Theory" and "acquired gossip theory", each with its own characteristics, but their connection with the sixty-four hexagrams seems to be incidental. Later, some people put forward the concept of "even pair, no repetition" for the sixty-four hexagrams, and pointed out some internal relations of the sixty-four hexagrams, but failed to systematically solve the problem of hexagrams order in the Book of Changes.