I am fortunate that I come from a creative family. My mother was/is an artist, specializing in Alaskan landscapes mostly. One of my sisters paints, another's a florist, another is crafty...the list goes on. Before I got back into writing and publishing I actually designed and created specialty greeting cards for people. It was an awesome job but not overly profitable and I am so hands-on that I printed them all myself which also meant folding, cutting...it was all a bit overwhelming.
Anyway...because of all that, I design my own covers and many of those for other books through the publishing company. Some, like Sharon E. Cathcart's "In The Eye of The Beholder" are designed by artists (James Courtney created her cover). Jaimey Grant designed the cover of "Deception" with an occasional "try this" or "try that" from me. My children's book "How Sadie Learned to SMILE" uses a cutout from one of the illustrations in the book. I created several backgrounds for it using that same illustration and bounced them to the illustrator until we agreed on one we liked. Video producer Patrick Sipperly designed the cover for our collection of short stories: "Time Out On A Roller Coaster". It was a concept he came up with and I happened to like.
I spent some time this summer creating book covers for several of my works in progress. Many of you know I hurt my back and was unable to sit to work for long. Oddly enough, I was able to hover over a mouse at my graphics computer so...that's what I did. I spent a lot of time browsing the pages of a site called Dreamstime looking for my characters. I would then pull them into the template I use and play until I got it right. Dreamstime has comp images you can use for free to see if they will work. At that time you buy the ones you like and the annoying watermarks go away :) An example would be this cover for one of my novels. It isn't finished but hopefully you can see the swirly watermark on the couple and on the girl in the frame.
Notice too that the front of the book is on the right and the back of the book is on the left. There's also that "dead" space on the back (To the right of the girl) where the bar code will go. You have to be careful about that...not putting anything there that you don't want covered. To see this in more detail, check out my OneStopPublisher.com Cover Creator Page. I don't have a lot of covers on there, though. I need to update it. I'll do that in my spare time!!!
Let's look at another cover. It's for an upcoming book of mine called "The Escort"...at least that's the working title. The cover (along with the lovely watermarks) shown here is basically 3 photographs sandwiched into one.
How was I able to look at those three pictures and decide they would work? I don't know. I guess that's the artistic side. Other than some minor tweaks, I do know, I love this cover and it expresses exactly what I wanted to express about what might be inside.
Now, do be aware that when you use sites like Dreamstime and others you may run the risk of others with the same pictures on their covers. Vicki Hopkins, author of "The Price of Innocence" has commented that she's seen her photo art on three other books, I believe. I personally love Vicki's cover and think it fits her book, so to me...it's a who cares.
The man in my Escort book (he's not the escort, by-the-way) can be found on another cover as well. Take a look at this one by Miss Mae. You know what? I'm okay with that because as much as he might depict her character, this man is my character as well. He fits too perfectly for me not to use him. Her book, "When The Bough Breaks" won a Best Young Adult Novel award and also a Best Cover of the Month Award. I've heard from a very good source that it's a worthwhile read. I can personally recommend "The Price of Innocence" as well.
Some artwork doesn't need a lot. Take the picture of the sword, for instance. We turned it into a cover for a soon to be released novel by Richard S. Wiggins, Jr. titled "Kilaal's Sword"...I sent the author a bunch of sword pics and asked which one. He chose this and I got to work. According to his instructions, the sword needed jewels placed strategically in the handle. That was actually the hard part. The cover turned out pretty good, in my opinion. The author liked it and that's the most important thing to me.
So, in answer to your question, Silvina, if an author does not have an artist in mind, I usually tackle the project myself or with one of the other designers through the publishing company. I would say that I'm not so sure I choose a cover or if, in many ways, it chooses me. More often than not, it has a lot to do with the author's tastes, the fortune to stumble across a great artist or perfect photo and a whole lot of intuition. Covers are as personal as the words on the pages they cover. I'd urge every author to browse sites and make a file of covers that catch the eye. Take a tour of your library or local book store. See what jumps out at you. Most of all, when you begin creating your own cover, whether you do it yourself or with the help of a professional, have something created that you love. If it doesn't touch you, how will you be confident enough to present it to others? The ultimate goal is to sell your book. You have to love your cover and believe in the contents to do it.