The optimal size for your images in pixels depends on the size of your book and the PPI (Pixels per inch) setting on your images.

Here is a table setting out the recommended image size in pixels, assuming you are using the recommended setting of 72 PPI: https://leanpub.com/help/manual#leanpub-auto-page-sizes-and-maximum-image-sizes.

You can see and change the size of your book if you go to your Book Tools menu, select "Writing," and then select "Book Theme."

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