title_body: Size of Epub Title Page (not cover)
upvoted_answer: There are no size constraint as such for images ( eg . title page or any other image), however it is preferred to have high resolution images.
  
  Note :  Just make sure if the book contain too many images, due to high res images epub size should not become too heavy.
  
  Secondly make sure as a best practice following styling is carried for all images
  
  All images width should be 100%:
  
  img {width:100%;}
  
  
  Bind every image inside a holder to control the size of the image as required:
  
  div.imgHolder {
  width: 85%;
  text-align:center;
  display:inline;}