It is getting more and more common that users are taking photos with their smart phones rather than a traditional digital camera. When taking initial photos users may be photographing upside down or in a portrait orientation. When these photos are imported into Image Editor the problem become apparent, but there is an easy fit to this problem.
In version 20 and higher, go to FILE >> MODIFY BACKGROUND and rotate the background.
In the previous versions, using the Rectangle Area tool, drag a rectangle around your background and create a new object. Next, click on the FLIP VERTICAL tool and select FILE >> FLATTEN PROJECT.