Actually it isn't the forum software, it is the device itself - Apple and Samsung being the biggest offenders. Since the original iPhone, Apple programmed the Meta Data incorrectly for portrait style photos (photos that are taller than they are wide). They coded the photo size in the Meta Data the same for both landscape and portrait style photos. Why Apple hasn't fixed this, I don't know. Some how, Samsung and a few other device manufacturers programmed their photos incorrectly too.
Web services like Facebook will re-write the meta data when photos are uploaded, so they always show up correctly. However, services, like this message board don't re-write the meta data so the photo is displayed based on the incorrect meta data. Editing a photo will re-write the meta data correctly.