If you take my advice and include a photo with every facebook post, you know that the photos don’t always show where you want them to. Fortunately, Facebook has recently added a “reposition” option.
After your post and been uploaded, click on the “Edit or Remove” pencil, then the “Reposition Photo…” option.
Depending if the photo is landscape or portrait, you can reposition the photo horizontally or vertically until you have a better composition to the square frame that facebook currently uses.
When you are finished, click the “Save” button.
While not a perfect solution, for most photos this should work. If you want it 100% control, you’ll need to crop your photos to a square, since that is Facebook’s preferred shape.