Nevertheless, in my world, an illustration is rarely required and almost never the most important element on the cover. What is? It could be the title, the subtitle, or the byline.
- The byline: If you're a famous author, the smart publisher will make your name the biggest, brightest, and easiest-to-read element on the cover. If you're not, skip to the next item.
- The title and byline: These two items dance together. If your title is sufficiently descriptive, it should dwarf anything else on the page. If your title needs help from a subtitle to describe who the book is for and what it will do for them, the title should remain the largest element (otherwise, booksellers and buyers may become confused about the actual title), but the subtitle should gain more prominence and perhaps pride of place at the top of the cover. If your title and subtitle are particularly strong, and they should be, your publisher may opt for a "type solution"; that is, no image at all. Before you write off this approach as boring, go into a bookstore (if you can find one these days) and check out all the mass market paperbacks and note the simplicity of the cover designs. They are mostly type solutions; most of the type is big and blocky and all caps. And then remind yourself that these are the books that sell the most.
Cover images, along with backgrounds and color schemes, are secondary elements that essentially create the right environment for the most important elements: your title, subtitle, or byline.--The Publishing Pro.