Most of my discussion so far has focus on two factors that strongly influence ebook covers: the need to work in thumbnail and the need to work in greyscale. However, it is also worth remembering that many ebooks are bought through a browser on a computer, not just through ereaders. Up to 70% of online book purchases are made at Amazon (according to the Bookseller’s Association). This means that ebook covers shouldn’t just look good by themselves; they should look good on the Amazon website. As most of the Amazon website is a neutral white this isn’t usually a problem, unless the book cover is white. If the cover is white, it will merge with the white background of the website and lose all definition. Rainbow Six and Kissing Freud are both perfect examples of how this can happen.
If the cover calls for a white background then the best way to make it work online is to add a border, to outline the image as has been done for The Man who Did Too Much. It’s also possible to define edges using other elements. In Lauren Takes Leave the cover is filled with images and text while in Watch Over Me the blue trees line most of the edge of the image. Where the edges are white the eye draws its own line, inferred from the lines that can be seen.