Fair use is basically an affirmative defense to copyright infringement. Whether something is fair use or not depends on four factors which are evaluated on a case-by-case basis. These factors include how much of the original work you used, whether the new work is transformative, whether it's a commercial use, etc. You can read more about the factors here.   Therefore, whether or not a cover is fair use can't really be said with 100% certainty, but we can make an educated guess as to whether a