Update 4/26/12: in just the last 24 hours or so, Amazon has updated the KDP interface: adding the product image as your internal book cover is no longer an option, it is mandatory. KDP help pages have been changed to reflect this.
A few weeks ago I wrote a blog post about Kindle’s new option to use your product/cover image as your interior book cover when you upload your book using the Kindle interface, as well as Amazon’s new guidelines for larger images, likely a response to the phenomenal screen resolution of the iPad3. However, questions arose as to whether Kindle is charging a higher delivery fee for those larger images; and what is happening with interior images, still limited to 127KB?
A query to Amazon has gone unanswered despite my repeated requests and their repeated assurances an answer is forthcoming, so I did a simple test to see if the delivery charge is increased if you use this option and upload the maximum image size for your cover, which in just the last few weeks has increased yet again and now sits at a preferred size of 2500 pixels on the longest side (and the minimum has increased to 1000 pixels on the longest side). The answer is good news: using this option actually decreases your delivery fee because the cover is no longer embedded in your file and Amazon do not appear to be charging anything for the cover if uploaded separately. For example, the original file of Baby Jane, which has the cover embedded, is .53MB with a delivery fee of $.08; the same ebook uploaded without the cover embedded and a 2000-pixel image uploaded separately came out to .48MB with a delivery fee of $.07.
This test doesn’t answer the remainder of my questions about future proofing, nor how the cover image is downsampled and/or compressed, and unfortunately the preview function on the Kindle interface doesn’t give a good indication of the quality of the cover image using this method, but on the surface of things it appears to be fine (downloading the HTML preview from Kindle doesn’t help as the file doesn’t include the cover image). I suspect that this method improves the quality of your cover image as it is likely the image is being delivered at a size commensurate with the device it is being sent to, as is what happens with Kindle books made using InDesign (for details on that, read the previous post on this issue), but as Amazon refuses to tell me if this is the case I cannot confirm my suspicions.
For those using Word, HTML, or Calibre to produce files for Kindle, then, it is now recommended that you do not include your cover image in these files and instead add the cover upon upload.
And what of interior images? At the moment these remain limited to 127KB, which means you still need to use smaller images because larger images will require too much compression to bring them within the 127KB limit. The exception to this, as mentioned in my previous post, is the use of InDesign to create Kindle books. If you are producing a book with interior images, you really should use InDesign or hire a designer who can, as otherwise your images on the iPad3 will be very small at their native size and will look terrible when expanded to fill its screen. I expect this 127KB limit eventually to increase as Kindle produces further developments in response to the resolution of the iPad3, but for now Amazon appears to have focused its efforts on the cover image as most ebooks do not contain interior images.