Oddly enough, Steve, when I clicked on your photo on my iPhone, it enlarged... with correct orientation! Tried the same trick on my iMac... still upside-down!
I then saved your photo into my iPhone photo app and found that it again had the wrong orientation (upside-down).
Next trick was rotating through 180° and reposting.
I can see the file size has been reduced, though.
What I have found, with my own iPhone, is that rotating something which appears correctly in my photo app but wrongly on the Forum website, is to rotate the photograph 360° in the app. I don’t know whether this would work with other kinds of phones, but it’s worth a try.