You have this dream of the beautiful cover art that will someday grace your novel. If you're artistic, you sketch or paint or scrapbook fanciful mockups of it. If you're not, you still create them in your mind. If it's your first novel, Da Vinci likely could never equal the masterpiece of cover art in your imagination.
Nothing, however, can equal the dream of the moment you first see what your publisher has wrapped around your story. You've been fretting about it for months, if not years, and at last the day has arrived. It's here. Here for all of publishing and the world to admire, and of course they're going to. Because it's going to be perfectly executed, exquisitely tasteful and wholly appropriate for the book.
And then? You wake up and smell the rainbow transvestite dolphin.
Books are identified by the general public with the author, not the editor or the publisher. The average writer has little to zero input or control over what's slapped on their cover, yet when the art goes horribly wrong, it's the writer who takes it on the chin and in the heart. And it takes a lot of spine for an author to voluntarily post an image of a novel in cover art hell for all the internet world to see.
During my rookie year I was told that writers have two options when it comes to cover art: 1) Never complain about anything they put on your novel, and 2) Never complain about anything they put on your novel. Although I've mellowed quite a bit in my old crone years and try to be more diplomatic when I pass along my opinion of my cover art, I do give my opinion. Even when I express concern for the lacerations it may inflict on my readers' corneas.
One insider tip: when an editor shows you a lot of cover art examples and then asks your honest opinion of them? Find out if she likes them first before you answer the question.
Bad cover art is not the end of the world. Most pro writers become resigned to having stories regularly sent to cover art hell as part of the job. If nothing else, it's best to laugh at it and move on. Maybe to a cave in Tibet where no one knows you wrote the book.