Hope you find this usefulHello Kevin,
In response to your inquiries regarding images within content:
1) PNG is a supported format, however JPEG (.JPG) will convert best
2) 300 DPI is recommended
3) The width and height should be 600*800 pixel
4) The image size should be 127KB
5) Use the link to find more information on reducing the file size: https://kdp.amazon.com/self-publishing/help?topicId=AQY9VBML4LKPK#decrease
I hope this helps! Thanks for using Amazon KDP.