You can add your favourite picture as well as up to four pictures in a collage to the cover of your book.
In addition, you can upload pictures, videos, voice messages and notes anywhere you want. How cool is that! 
Desktop: Activate ” Add media” located in the right upper part of the chat edition page and click on one of the plus signs
Mobile: Click on the plus symbol and then on one of the plus signs
That way, you can not only print WhatsApp, Facebook Messenger, Instagram, iMessage, Threema or Telegram messages but also any other chat content you want to create yourself!