We all know that expression, "You can't judge a book by it's cover." While that may be true in terms of what exists inside the pages of the book, if you are trying to get people to buy your book to find out whether the words are as wonderful as they are, then you need to think about cover art. Whether we like it or not, people do judge a book by its cover and their appraisal of the cover greatly influences their decision to buy your book, or to pass.
Professional authors and publishing companies will spend hundreds of dollars or more working with an artist to create a professional looking cover. Most self-published authors may not find this an affordable route but that shouldn't stop you from creating something attractive. Familiarity with a photo editing package like Photoshop or the GIMP can go a long way to creating a great cover. Ensure you have the right to use the cover art you choose (there are many public domain images out there), and don't forget to include your name, as well as the title of the book.
So what is a good cover from a technical standpoint?
Most eBook readers use a 600x800 pixel screen. Creating a cover with those dimensions in mind is a good idea. That said, the dimensions of a typical paperback novel is closer to 5 by 8 than 6 by 8 and looks more natural. That's roughly a ration of 1 to 1.6 for whatever resolution you use.
Higher resolutions mean crisper images but larger file sizes. Too small an image and the reader can't tell what's on the cover. So following the above rule, try to make your cover 500x800 pixels or greater using the same ratio. For example, 600x960 or 1000x1600 (don't go any larger than this last).
In terms for format, save your image as PNG or JPG.
The last item you should consider is that many devices are E-ink readers which means your super-amazing cover should render well into grayscale. Strange, hard to differentiate combinations of fonts and artwork may not look great. If possible, test drive your cover on an E-ink reader before you put your eBook up for sale.
Authors using our conversion service will find that a cover image is optional. If you don't specify a cover, our system will generate one for you with our default cover art, your name, and the title of the book.