Images can be used within a book or on the over as a book, where it's part of a bigger body of creative work, bearing in mind the below limitations.
For information on using images as the cover of a notebook, diary or other product please read https://help.unsplash.com/en/articles/2612317-can-i-use-unsplash-photos-as-part-of-a-product-to-sell.
There are limitations when it comes to commercial use of Unsplash images, like as the cover of book.
Note that the Unsplash License does not include the right to use:
Trademarks, logos, or brands that appear in Photos
People’s images if they are recognizable in the Photos
Works of art or authorship that appear in Photos
If you download photos with any of these depicted in them, you may need the permission of the brand owner of the brand or work of authorship or individual depending on how you use the Photo.
Please review our License for more information and, if you still aren’t sure, you should probably talk to a lawyer who knows about these things.