Thank you, Peter.
I prepare my images in PhotoShop. I make them 6 inches wide (usually) and 300 dpi. I don't adjust their size in Pages. Aside from this, please, what else should I do to set "real" size?
PNG vs jpeg: But this doesn't relate to Pages reducing images to 72dpi, right? I prefer PNG because I work mosty in video, where jpegs are dangerous because they have two fields and often don't keep the field you select (which can turn a smile into a sneer) or flicker.
Transparency: none of my images overlap anything else, nor have shadows, reflections, frames or 3D.
All of my images are reduced in dpi when I export from Pages, no matter which export route. The Pages document is 680MB, the export versions are 120-150MB. (There are 700+ images in 733 pages.)
When you upload to Kindle (print, not ebook), your next step is "Launch Preview (NOT the Apple application)." In Launch Preview Kindle indicates which images are less than 300 dpi, and about 200 of mine are 72-115 dpi, even though in PhotoShop/Pages they were 300dpi and 6 inches wide.
Kindle upload permits pdf, doc, docx, rtf, html. Not Pages, alas. But after several dozen tries, the only format that reaches the Preview stage is pdf. In all others, "error" is cited.