Here's a rescue for self-published writers lacking training or talent for book-cover design, but who must design their book covers anyway: Canva.com. I tried it and liked it, re-designing a book cover for an ebook, and it looked much more professional than did the previous cover, which used Kindle's cover tools, and it was easy. Canva.com has fonts and a bank of 1 million images, or you can upload your own. After your cover is finished and downloaded (as a PDF or a zip file) you have 24 hours to return to the site and tweak it.
The free-image bank at Canva.com is lame, and they know it, so there are other images you can purchase for $1. You pay and then they'll let you download your book cover. I spent $3 on a cover design that took me 30 minutes (most of that time looking through the image bank) and is 100 percent better. See the "before" and "after" at right.
Canva.com also has design tutorials and other helpful information.
Self-published books too often have poorly designed covers--not because the author wants it that way, but because the author is an author, and book-cover design, which is a marketing tool, is best done by professional book-cover designers. My one rule for authors designing covers: No amateur images. That means not your daughter's painting, not your snapshot of a barn, not your own photo (a book is not a music CD). Those are death to your book because they're about you. After a book is published it isn't yours anymore. It belongs to the market and the readers.