This is the answer I received from Tech Support when I asked a couple of weeks ago:
"Most pictures these days come straight off our phones. The phone's software embeds some coding into each image when it is taken. This code tells the phone which way is 'up' and displays it correctly for you. Unfortunately, that coding cannot be read by the most forum software and so the pictures appear whichever way they were taken with the phone.
"There are some tips to get the 'correct' orientation for your photos on your phone.
Android users take photos with the HOME button to the RIGHT.
Apple users take photos with the VOLUME button DOWN.
"This is the 'correct' orientation for pictures on your phone. The developers base this off of a DSLR camera that takes photos in landscape mode as a default. So when you take a picture with your phone in portrait view, it's like turning the DSLR camera to the side to take a portrait photo.
"You can also open your pictures in an editor on your computer and manually rotate them. If you use an editor on your phone, you may need to crop off a couple of pixels, or save a new name so that a change is registered.
"You can also use photo hosts like Imgur, that have the software needed to read the coding on the images from the phones."