What is the most effective method for including illustrations in a Kindle ebook? And what is the preferred DPI and file format?
DPI/PPI settings aren't used in the web and are based by pixel dimensions and several web images
You also didnt mention how you are including the illustrations in the ebook. Are these vector or scanned images?
If you have built your illustration in either Illustrator or Inkscape I would use an
I would use
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.
There's plenty of information about this in section 3.6 of the Kindle Publishing Guidelines. To sum up:
Personally, I avoid .png when possible, as they seem to end up substantially larger than .jpg files.
I just wanted to add that latest version of the "Amazon Kindle Publishing Guidelines" PDF (updated 1/2014) http://kindlegen.s3.amazonaws.com/AmazonKindlePublishingGuidelines.pdf can be downloaded for free from the Amazon site. This last revision contains a lot of updated recommendations for images.
With the recent guidelines Amazon has changed their philosophy a bit on images (and that is good). Kindlegen performs automatic image conversions, so the guidelines suggest that you can use images of up to 5mb for interior images.
As it happens, I'm currently trying to convert my interior jpg images to svg for reasons of scalability. Amazon's support of SVG seems "adequate" now -- although SVGs are their own kind of beast.