(adding a reply to turn on follow-up email notifications)

Thank you

I had incorrectly specified jpeg conversion on the epub & html section of the Object Properties. Changing to png results in png export as intended. Even when I unzip the epub, replace the png with a transparent one, and epubpack to reassemble to epub, the image displays in Kindle Previewer with a white background.

Any other ideas?

Great suggestion. I unzipped the ePub and discovered jpeg images instead of png. No wonder they’re not transparent.

What causes InDesign to convert images from png to jpeg when exporting to ePub?