title_body: How should you include illustrations in Kindle ebooks? What is the most effective method for including illustrations in a Kindle ebook? And what is the preferred DPI and file format?
upvoted_answer: DPI/PPI settings aren't used in the web and are based by pixel dimensions and several web images .png, .jpg, and .gif files sometimes do not include the settings in the internal data.  
  
  You also didnt mention how you are including the illustrations in the ebook.  Are these vector or scanned images?
  
  If vector:
  
  If you have built your illustration in either Illustrator or Inkscape I would use an .svg file format but that is a personal preference.  From my understanding, .svg format can be a less file size than exporting the illustration as .jpg or .png.
  
  If images:
  
  I would use .png files because they can be compressed and help reduce your file size.  A good compression tool is Tinypng.  If you're wanting a command line compression tool there is pngquant but I havent tested it yet.
  
  To request what type of method is most effective would depend on how you tend for the ebook to be viewed.  It is common for illustrators to use fixed layout to control how the illustration is viewed.  This is common with children's books.