Now, I really have uploaded the book in a format that works. I've tried it on Apple iBooks, Barnes & Nobles Nook, Kobo, Sony Reader, Books on Board, Marvin, and Kindle. All except the Kindle were uploaded to Smashwords, which does make a Kindle version but doesn't send the book to Kindle. It's an option to buy on Smashwords, but it doesn't work as well as the actual Kindle version. All the other versions it made for programs that use the .epub format worked well. The contents link to the pictures before the chapters, and the centering of the images and text works now.
Some of the centering problem was actually because of the programs themselves. Nook, for instance, has an option to use the publisher's formatting or Nook's. If you set it to Nook's formatting, Lmost all of the centering is lost. On publisher's formatting, everything looks perfect.
I really like Apple's iBook because you can set it to look like a book. The pages turn like a book, and it looks really good to me.
Sometime, I'll write a comparison of the different ebook readers I have, and maybe I'll try to get a few more in the meantime.
Anyway, I succeeded. My next book should be much easier to format! For now, I have to go do some bushcuttering and then pay some bills and then...