If you have a ton of photos that are all facing the wrong direction and don’t want to do them individually, you can use Hazel to automatically go through a folder and rotate the images for you.  All it takes is a one-line bash script and a Hazel rule.

sips -r 90 "$f"

This rotates the image 90 degrees.  You can set it to 180 or whatever else you want.

Another great Hazel rule is to resize large photos automatically.  You can use sips  for a lot of other stuff, too.