Do pictures even make sense in a Kindle ebook?
Images won't make sense if your readers are reading on a Kindle with an eInk screen. Graphics and tables maybe, yes, but pictures probably not. A regular Kindle can only display 16 different shades of gray. Standard images are therefore out of place here. However, potential buyers can also read the books via an app in their browser, tablet or smartphone. Now pictures in colour with good resolution make a lot more sense. Now please don't clap all the visual material into the ebook. There is a lot to consider!
Earn 35% or 70% royalties on Kindle Direct Publishing
Before you even deal with pictures, you must clarify one question in advance. Would you like to have 35% or 70% of the sale proceeds for your books later? 70% probably I would have taken it now too. There are pros and cons here, though. If you choose the 35% royalties model for your ebook, you do not have to pay any shipping costs (transmission costs). But you are limited in the selling price.
If you choose the 70% royalty model, you must deduct around €0.12 per megabyte of book size. If your book is vast and contains a lot of pictures, this can add up to several megabytes very quickly. It is, therefore, worthwhile to calculate which model is more lucrative for you.
Extra Tip: Optimizing the images directly impacts your profits when selling Kindle ebooks. That may not matter much when you've sold an ebook, but overall every saved megabyte pays off.
The proper image format for Kindle ebooks
A Kindle can handle the following formats: GIF, BMP, JPEG, and PNG. A single image file must not be larger than 127 kilobytes. I always use a resolution of 600×800 pixels. The readers sometimes have very different answers, but most authors seem to be doing well with this one. Anyone who wants to cover iPads is well positioned with an image width of 1024 pixels.
As already mentioned, the eInk screen in the Kindle readers only displays 16 shades of gray. If you want to align your images with this, turn the contrast. This improves the display on these devices.
The PNG format can save shades of gray with a colour depth of 8 bits. Here you get even smaller files than with GIF files. If you want to insert images with a transparent background, then PNG is the file format of your choice here as well.
The GIF format is perfect for grayscale images or line and table graphics. This image format is ideal for making fine lines easy to read.