Tip 1: Save yourself some headaches and keep a separate folder with a copy of all the latest artwork and images, for both the front and rear cover and all images internal to the document. It’s really easy to lose track of different versions and file locations. Later, if an image needs to be modified or the resolution changed, you can easily find the right file. Name the file the same as the image used in the epub.
– Greg Lundberg, Quicksilver Books, “How To Publish An Ebook For Under $350,” March 2012.