Willing to bet you are taking the photos with a mobile device like a phone? They have a "correct" way to be held when taking photos that they don't tell you. As long as they are on your phone it doesn't matter, but once you try and upload to the site things get screwy.
For photos you have already taken, upload them to a computer, rotate them once, save, rotate again to the way you want them to face, then save again. This will fix the photo file. For photos taken in the future, try and make sure you hold your camera sideways, with the home button on the right side.
All that said, if I bet wrong and you are using a regular camera, let me know