Forum Moderators: not2easy
The safest way to proceed would be to contact the book publishers and clear it with them. More than likely they will be very pleased for the opportunity of publicity.
(1) ensure that you can use the image under terms of fair use, or if not, ensure that you have permission ("a license") - for the former you do not need to ask [although the image is a photograph that you have taken, it would still be considered a derived work of the book cover, there is a separate copyright that exists in the image, but that separate copyright may be an infringement of the original];
(2) ensure that you identify the source, which you seem to do;
(3) ensure that your context of use of the image doesn't cause problems (e.g. you are not misrepresenting what the book is about, or other attribute of the book, or something about the publisher/source);
(4) ensure that the nature of the image itself doesn't cause problems (e.g. if you had created a poor quality image, despite being under terms of fair use, in particular circumstances, the owners of the material could take again substandard quality or "passing off" issues, because you may be creating negative goodwill to others about the nature of their property right).
Matthew.