ebook - place of copyright information?

In the licensing terms, Adobe says, "at an appropriate place" (bold is mine).

(B) you must include the accompanying credit line or attribution, placed in a way that is reasonable to the applicable use, in this format: “[Contributor Name]/stock.adobe.com”, or as designated on the Website;

With books, the credits are very commonly grouped at a specific place.

Look here for more information on licensing: https://community.adobe.com/t5/stock/links-for-licensing-terms/td-p/11366788
(Disclaimer: As always with licensing, this is my interpretation of the rules. I think they are correct and advice is based on reading and interpreting the licence terms and on fair use for both the buyer and the artist/stock company, but I cannot rule out that my interpretation is wrong. I'm not an Adobe employee).