Bagged to rights.

[Katia]

My guess, Jock, is that it was sideways all along and your photo viewing software detected that it was sideways and automatically flipped it right-way up for you when you looked at it on your computer, so you assumed that was the natural orientation. I know it happens that way on my computer... and I forget I had taken it sideways, and then I upload it somewhere and end up having to go back to edit it and re-post it.

[Jock Scot]

My guess, Jock, is that it was sideways all along and your photo viewing software detected that it was sideways and automatically flipped it right-way up for you when you looked at it on your computer, so you assumed that was the natural orientation. I know it happens that way on my computer... and I forget I had taken it sideways, and then I upload it somewhere and end up having to go back to edit it and re-post it.

Aha! That makes sense, thank you.