Thank you all for your helpful comments.
I bit the bullet and bought the Kindle version of the book, so I could see also the inside pages.
Well, there was a credit notice for the image at the last page of the book, attributed to myself and Dreamstime, the selling stock agency.
However, my initial problem was that the image on the cover was displayed without the credit notice, and all Amazon visitors can see only that page, not the page with credits inside the book. Such is obviously the nature and disadvantage of the digital implementation and presentation of the ebook that was never an issue with the physical paperback.