Launch a graphics package on your computer. If you don't have a graphics package, GIMP or Paint.NET can be downloaded for free, or you can use a free online service such as Pixlr.
Create a new image that's 900 pixels wide and 1250 pixels in length. Fill the background with a solid color of your choice or a gradient.
Create a new layer and draw a rectangle in the upper half of the background. Fill the rectangle with a contrasting color to the background, and add a stroke of approximately 10 pixels to give it a wide border.
Select the text tool and add the e-book title and writer's byline inside the rectangle. Use a large, easy-to-read font.
Create another new layer and import a relevant piece of artwork for the theme of your book, positioning it in the lower half of the background. Resize the artwork so it mirrors the rectangle in the upper half, adding the same color and size of stroke to give it a border.
Save the image to your computer as a JPEG file.