After having a novel published, I decided to publish Lives Interrupted myself using KDP and Smashwords for the electronic version, and CreateSpace for a print version. I documented the steps I took and what worked best, and earlier this year decided to pull those posts together in an electronic book Smart Formatting.
About a month ago some of the requirements for cover images changed and I've updated the dimensions and information in Smart Formatting.
Below is the new information.
In mid 2012 Smashwords changed the minimum image pixel dimensions, as Apple required higher pixel counts. They require all ebook cover images to be at least 1,400 pixels wide. If you are looking for a good height to width ratio, say 1:5, you could go for an image of 1,600 wide by 2,400 tall.Normal service will be resumed in the next post, and I'll continue with positive and negative character traits.
KDP has a minimum of 1,000 pixels for the height and state an ideal ratio of 1:6. They recommend that images be 2,500 pixels high. For this ratio you could create an image of 1,600 wide and 2,560 high. The image must be in RGB (Red, Green, Blue) colour mode. I uploaded my image as a .jpg file although KDP say they will also accept .tif files.