Thanks for reaching out to the Adobe Stock community.
Generally, using an image on the cover of a book(with a standard license) is OK as long as the primary value of the book isn't based on the image. Although the print run must be less than 500,000 copies also.
However, if the primary value of the book is the images you will be requiring an Extended license.
Please refer to the licensing terms and restrictions of Adobe Stock Stock Licensing & terms FAQ: Where can I find the terms and licensing information for Adobe Stock? for more information.
Feel free to update this thread in case of any additional questions,
Thanks for your reply.
To me, every book's value depends on the content and description of the book, then the cover, but the cover attract the readers to it.
But just for one last time clarification before I start buying the images with standard licence. The book will be published on Amazon Kindle, still can I use get it under standard licence ?.
I would suggest you to go for an Extended license because the book is any which ways sold.