I work on a Mac in Safari, Firefox and Chrome and on all 3 browsers the image was rotated horizontally.
When I looked at the pages on my iPhone and iPad, they were rotated correctly (vertically).
Looks as if its an EXIF data issue with WordPress. Here are a few other instances:
http://wordpress.org/support/topic/image-rotation-issues-and-incorrect-mobile-browser-display
http://wordpress.org/support/topic/uploaded-photos-not-being-automatically-rotated-according-to-exif-data?replies=12
And then there is the BuddyPress fix:
https://rtcamp.com/rtmedia/docs/fixing-image-orientation-wordpress-uploads/
I’m not a programmer, so I do not know how to apply this myself. Perhaps you guys can consider writing it into the next upgrade.
I would imagine, there may be quite a few people who upload photos from their phone these days.