Amazon sent out an email today detailing a few features recently added to Kindle Create. The app still can't make a Kindle ebook that you can read on your Kindle (it can only make project files for you to upload in KDP) but the email did point out a new feature that is in beta.
Kindle Create can now insert an image so that it is full-bleed. In print terms this means that the image would be printed to the edge of the paper, but when it comes to ebooks full-bleed means that the image will be displayed at the edge of a device's screen.
Our new image formatting features allow you to insert, place, and resize images in the way that best suits your eBook. Learn more about Kindle Create, image handling features, and Early Access available in Kindle Create 1.12. You can also try out a new Early Access image bleed feature that enhances Kindle reading experience by extending the images to the edge of the device screens.
I've been testing this feature for a while, and from what I can tell this is only available with reflowable Kindle ebooks, but not Kindle's PDF format. Given that you can insert a full bleed image in your source PDF before loading that PDF into Kindle Create, that is no big deal.
I haven't had a chance to test the full-bleed image on an actual Kindle app or ereader, but I did confirm in the previewer that the image did appear to stretch from one edge of the screen to the other.
Unfortunately it is a both or none situation; you can't have the image at one edge of the screen and not the other. Also, using this feature locks the ebook into a portrait orientation, a good trade off given that the image is so much large than before.
Remember, most of the images in a Kindle ebook are affected when the user changes the margin settings, but the full-bleed images are not. One of the benefits of this option is that it means that the image won't shrink to illegibility when a user switches to the max margin setting.
You can find out more about Kindle Create in KDP's support pages. The info is rather sparse.