In reply to davegs:
It's probably already landscape, and whatever software you use to view it auto-rotates it for you. When you upload it, it will keep its actually orientation rather than the one your software detects for it.
The moderators have an option to manually rotate an obviously wrong photo, but it doesn't always get used.
The other possibility is that you intended it to be the wrong way up, but a moderator noticed and helpfully correct it it for you
