I had an email from a client, about his cover—he wanted us to remove it from the eBook we'd made for him.  As he explained:

"As to the cover, I am concerned that the cover becomes part of the ISBN, so that (copyright) challenges to the cover would undermine the ISBN. And since Amazon has a process for an author using their own cover, I figured it was sensible to take the cover out of the file. That way, I can easily change out the cover if Amazon objects to it.

So please take the cover out"

Wowza.

Now, there's a lot going on in that email.  First, the person in question is conflating copyright with ISBNs, and moreover, then conflating licensing (for images, apparently) on top of that.  

Your ISBN has nothing to do with copyrights. It exists, primarily for print books, for the purposes of ordering, fulfillment, sales and payment.  In ye olden days, it was common for thousands of copies of books to sit at distribution centers.  When Jane would send an order from her bookstore, for the "paperback copy of 'Love's Savage Fury'," perhaps she'd get the trade paperback; perhaps she'd get the mass market paperback.  The concept of ISBNs—a single unique identifier, for each edition of a given book—gives booksellers and publishers a way to be certain that the right book is being ordered, and delivered.

Of equal, if not more, importance, the ISBNs belong to the book's publishers.  That way, when Jane looks up the mass market paperback for good old "Love's Savage Fury," and uses its ISBN to order it, the distributor or warehouse knows exactly which publisher is getting paid—because the ISBN for that particular book is owned by the Bippity-Boppety-Bo Publishers.  This is an important concept—ISBNs are purchased by Publishers. The books which are published under those specific ISBNs are all published by that specific  publisher. That's how publishers make sure that they're being paid for the books that they publish.  So, again:  ordering, fulfillment, sales, and payment.  Those topics have nothing to do with copyright.

Copyright has to do with your intellectual property, and how you protect that. It has precisely zero to do with ordering, fulfillment, sales and payment.  Your copyright exists the moment you complete your book, under US (and many other countries') laws.  What you think of as "copyrighting" your book isn't; it's registering your copyright.  You need to copyright your book, in the USA, because you cannot file a lawsuit for copyright infringement before the copyright is registered with the Registrar's Office.  That's the law. Thus, make sure you save up $35.00, so that you can register your copyright at ECO, the Electronic Copyright Office.