So on the back of the "ReeliChat Guide" item, a few players that were around at the time go their avatars on the back of the book ( including me ), and my idea is that the images change whenever the players change their avatars, to keep up to date with their looks and to know who they are.

Or..

If you are on the book, you can pay a certain amount of cubes to have it update your avatar on the book.