Unless you're viewing on a REALLY big high resolution screen and zooming in...
You probably won't notice the difference.
Looking at some of the books it's weird where a full page image isn't all that big, while a small icon of a dog that the author added in their about section is 4x larger than the full page image (
and like 10Mb by itself when it should be like 20k). Optimizing the images scales them and compresses them to match the display size. I'd assume it assumes 300dpi or something.
Anyways, they are scattered throughout (
use the search for the book name(s) and this thread); I'll also re-upload books you're interested in. But i tend to use that space for downloading content in a batch from certain sites that heavily use it.