Book Mockup Creator
As a Graphic Designer and Website Designer, I work with a lot of authors on their websites and book design. Most of the time they don't have mockups for their books that show the 3d version of the book, so I create mockups for them so it looks like a book standing. I usually do this with Photoshop but I recently found this free mockup creator that generates medium resolution book mockups from an image uploaded, you can even upload spines! Very quick and easy to use. You can pay for higher resolution downloads as well, but the free ones work great for websites.
smartmockups.com/mockups/square-books is a user-friendly only tool that quickly creates mockups of books and lots of other items.
I love it!