Cover for e-book

I've been trying to figure out a cover for my book, which to me has been more difficult than I had assumed.  I see all kinds of great covers on the Nook, and didn't really stop to wonder how exactly people were creating these covers until I realized I would need one myself if I plan to publish it anywhere.  I'm still not exactly sure how people are creating their covers.  I would assume some people hire a professional to do theirs, but it's my project, so I decided to go it my own way...so I've been looking up pictures in the public domain.  I have found three different pictures I like so far.  The first one was a cloudy gray sky, but when I slapped my title on there, it was just too washed out looking.  So then I found a picture of a pink cloudy sky with a sliver of a moon, which was neat looking, but I didn't feel like it did enough for me or would do enough for a perspective reader.  Finally I stumbled upon the coolest picture of a girl, who could definitely pass for the image I have in my head of my main character!  It's not just any picture though...It almost looks like the paint is peeling off the canvas, and the colors she is painted in are very earthy colors, which is an added bonus because my book has an element of nature in it, specifically having to do with flowers and herbs and their healing properties.  I'm very excited I found this picture, as I feel it's the perfect cover for my book.  It's mysterious and beautiful all at once...I would hug it if I could!  I discovered it at:  http://www.publicdomainpictures.net/view-image.php?image=4186&picture=decompose  I don't know who is responsible for this materpiece, but as it is listed as free for use in the public domain, I would just love to give a big shout of thanks for making my day!  And here is the tentative cover: