Book covers and their artwork are protected under copyright.  Companies, such as Brodart and Amazon.com, obtain releases from the copyright holders in order to publish these materials in catalogs and on Web sites.  Those rights do not pass on to the viewers/users of those materials. 

However, within the limits of the photocopying guidelines, a single copy could be made for a classroom or media center bulletin board, but could not be posted electronically, since this would constitute wide scale publication/distribution.  Similarly, a student could utilize a copy of one of the images in a report prepared for a class.  The photocopying guidelines, for making multiple copies for classroom use, would apply when creating bibliographies. Keep in mind that the guidelines indicate that one may take, at a minimum, (no clear statement of the maximum) one copy of  a picture, photograph, drawing, etc., from a source, to use in a classroom and that this is a one time only privilege, requiring permission when one wishes to use the material again.  When that time for permission writing occurs, contact must be made with the copyright holder.  Any commercial use of these images or incorporating them into works that will be distributed or marketed, with or without charge, is not copyright permissible without prior permission.

Please note that one should give full credit to the source, which, in this case, would be the copyright holders of the book, but acknowledging the on-line source from which it was obtained.