I've been reading quite a bit into the licensing terms on a variety of websites and would like to offer my two cents on the subject. It appears that images from Adobe Stock (under the standard license) can only be used for marketing, promotional, or internal presentation or decoration purposes, as outlined in section 2.1 of the terms. This means you cannot incorporate the images into a work that is of your own authorship, as that would make the work a derivative work (a work contains the copyrighted work of another). To include an image in derivative works, an extended license is required as outlined in section 3 of the terms. So while you could use an image from Adobe Stock on a book cover to help promote the book, you cannot use the image inside of the book, among the text, to contribute value and meaning to the work under the current terms (which I've found to be rather limiting compared to other sites), as that would be using the image inside a separate work that is your own (i.e. a derivative product). Essentially, with the standard license you can only use Adobe Stock images as stand alone images (with minor adjustments, such as text) and not as a part of a greater work where both the image and text depend on one another to create meaning and value. Perhaps someone from Adobe can affirm or clarify.
Paul365, thank you for such a clear answer. I think your interpretation is correct, and I'm going to have to shop elsewhere where the licensing is more clear. If what you say is correct, though, then their own advertisement for Adobe Stock possibilities (check out the island with tower, water fall, etc on their main home page - shown below) is misleading. When I look at this image I get the impression that I can clearly take several stock images and create something of my own (ie. a derivative product). I don't seem much of a difference between combining multiple images to create something of my own, or combining words and images.
Another interesting thing I discovered is that Fotolia is owned by Adobe. Some of the same photos are available on that site, and the licensing seems to be more clear. It's just not integrated into the CC product line.
Interesting! Thank you both for such an immenseclear answer. I wanted to use Adobe Stock but now I will just check out my library of congress where everything is free.