Most pictures these days come straight off our phones. The phones software embeds some coding in to 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 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 pixels, or save a new name so that a change is registered.
You can also use photo hosts like Photobucket, etc, that have the software needed to read the coding on the images from the phones.
I hope this information helped you out!