Amazon has a lot of info available for doing your own Kindle book. (I've done a few.) Here's a page on images:

https://kdp.amazon.com/help?topicId=A1B6GKJ79HC7AN

Basically up to 5 mb, 9:11 ratio. The attached photo, the inside title page of Kali, done in Poser and Photoshop, is 1002x1502, and it filled the page nicely. I've also used 1200x1920. 

You got to rather explore their info pages to find what you need--they dont seem as well organized as they could be. But the information is there.

If you get their free Mobi creator, you can preview your finished work and adjust the sizes.

 

 

 

Poser Pro 2014

My personal website: Novels, photos, video, sculptures and more
Evidence of a Lost City: An animated movie and novel, in progress
Hag: A novel and live-action movie