Someone asked me how I made my header for this site, and for The Virtual Bookcase, (WordPress removed the suspension and agreed the site was genuine!). Anyway, I noted that WordPress suggest 960 x 260 pixels for sizing. Then popped over to my favourite playground, PicMonkey.
I also use a site, IAZA. It has many other fun edits for your pics.
Back over to Iaza, and I had another play!
They are free resources that can help enhance your posts, and assist with marketing your books. Just don’t forget you have writing to do!