I aim to get my books published by a company but I am wondering about the cover design. Does the company organise the design or is it optional to do it yourself, or to get another person to do it? I would like a friend of mine to do a cover but is this not an option?
As I understand it, a traditional publisher has complete responsibility and authority for the cover design.
Yes, trade publishers have professionals doing cover design/selection. Some will give the authors input, but unless the author absolutely hates the cover, the publisher has the last word. Authors typically forget that it's not "oh that's pretty!" that sells the book, which is why publishers are generally better at those things.
you can only do that if you self-publish... or, if you have enough clout with your traditional [= 'paying'] publisher that they'll agree to look at your friend's work and consider using it...
A novel's cover is an important marketing tool. A good/professional one will enhance a books chances of success while a poort one will hinder chances of success. Publishers handle hiring an artist and make sure of the layout and titlework. While some authors are artists or have friends/family who are, most know very little about creating an effective cover. Smaller presses are known to allow an author more input. My publisher allowed me to suggest artists for one of my titles accepted for publication. I'd worked as an editor for a small magazine, and an artist that had won a cover art contest there struck me as a good candidate. So I suggested her to my publisher, and it turned out she has created the covers for both novels in the series and has been contracted to create the cover art for the third novel which should be released in June. With larger publishers, there is far less input, as least as I hear it from those several authors I know who've been regularly published.
It might be worth asking your publisher. I'm sure most would be willing to at least listen to your suggestions. A lot of thought goes into the design of book covers though, and most publishers will know best the kind of covers that will help your work to sell.