title_body: Centering images and text in ePUB and Kindle ebooks
upvoted_answer: You will probably run into problems doing it that way, particularly on iBooks. The most reliable method I've found for centering is:
  
  &lt;div class="centered_image"&gt;
    &lt;img src="image.jpg" alt="Alternate text" /&gt;
  &lt;/div&gt;
  
  
  With css like this:
  
  div.centered_image {
    width: 60%;
    margin: 1em 20%;
  }
  div.centered_image img {
    width: 100%;
  }
  
  
  On a very few reading systems (notably the nook), this can cause problems on some images due (I'm guessing) to rounding errors, so you may have to set the margins just a hair smaller (like 19% in the above example).