Sheila M - if you read this... I really see no point in your post, you do not attempt to give advice, just a link - to I cannot find the answer to my question and a bunch of FAQs. If the FAQs do not give the answer...( And the page you offer - does not) it means the op is left floundering and more confused.
The majority of questions are posted only after attempts are made to find answers and to be frank I find trawling around Apples support pages and links - not very effective or reliable in most cases.
The link you provide does not give any information on the ops question - leaving only a choice of "contact support".
I thought these support groups are to take the strain of support by assisting newer memebers with advice , help and information and leaving support staff to deal with other issues.
The answer to the question - at the least - should be in the help files under Graphics and Media..... but it is not!
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Front cover: 1400px minimum width @72PPI height if usually about 1830.
The Asset Guide giving full information for all content details and requirements can be found and downloaded from.. your TunesConnect > Deliver your Content - top right of page find a number of PDF downloads.
There is also a superb Keynote video for iBooks Author.