The question was asked about how to properly prepare the icons for your ebook app so it can be published. So here's some instructions and some tips!
Inside TaleSpring in the editing environment, choose Book on the top right, and then click Edit. On the properties screen that comes up, you'll see the list of icons that are needed along with the sizes and formats. The (?) images offer additional information.
As far as the actual image that goes in the icon, I highly recommend a zoomed-in view of one or two of the main characters rather than a shrunk down scene. This is an icon, a small representation of your app. Your designer/illustrator would have some great ideas for the icon as well.
All sizes should be the same image, just at different resolutions. The only exception would be the 512×512 where you can have more on it as long as it's not too different from the other icons. For example, if the app icon was of the main character's face, the 512×512 could be of the entire character, with part of a scene in the background, or something. Think of the 512 version as a zoomed out, wider look at the same scene the smaller icons were taken from, but not zoomed-out too much. If they're too different, Apple will reject the entire submission.