Harnessing the Power of EXIF Rotation
It might be hard to believe but there was a point of time when digital cameras cannot sense when you rotate them to take portrait photos and in the case of a smart phone, landscape pictures. Now all modern cameras come equipped with an orientation sensor and store this orientation information inside the JPEG File header or more technically known as the Exif header. Exif stands for Exchangeable image file format.
On a smart phone such as the iPhone, the photos will always show up in the right orientation because the built-in photo viewers read this settings but when posting the pictures to websites, it may not show up correctly and thus doing a real orientation change is needed.