I notice that the position of the nav bar has changed, and the smoke in the header has disappeared?
Have you recently updated to Ghost 3.0 or above? The smoke image was part of the default design in version 2.x
Oh right, I liked the smoke! And yeah, I just downloaded a fresh install so that must be it.
I just jumped into my time machine and got the smoke image for you:
You can upload it in Ghost admin under General settings > Publication cover