I need to find a picture large enough. It needs to be at least 1000 pixels wide. This one is 1024 x 819.
The header for this blog is only 288 pixels tall, and if I don’t edit this picture to show exactly the part I want (aspect ratio 1:0.288), WordPress is going to take the header out of the exact center of the image. In this case, the auto-crop is not bad, but I could refine it in a bitmap program such as Photoshop or GIMP.1
Another citation here. 2