are still the Recommended dimensions of the book cover picture 2500px × 3750px? even if the image in the book cover page is 800X600px?
Lots of different recommendations: http://www.ebookcoversize.com/
We chose a higher-resolution size to ensure that the image is always big enough for various ebook formats (you can always resize an image to make it smaller but you can never make an image that’s too small bigger). Maybe could be revisited.