Incorrect image orientation when posting images from iPhone to various forums

Sometimes when I upload an image shot on my iPhone to online forums, the image comes up with the incorrect orientation: an image shot in portrait, taller than wide, shows up rotated 90° to landscape, wider than tall.

I found a post in one of my forums where I'm complaining about the same thing from a phone and several iOS Versions ago. But today I am looking at an image that I shot in portrait orientation on my iPhone, that my iPhone recognizes and displays in portrait orientation, but that is showing up in landscape mode when I preview the post on the phone.

Little more play shows that it is happening with Firefox for iOS and Safari, so not a Firefox or Safari issue, but rather something that creeps in when I attempt to save bandwith by uploading a smaller size of the image. So whether I use Safari, or Firefox, if I select a smaller version of the image--not a crop, but instead of selecting the actual size, I select one of the other options, so a resizing--the problem occurs. So the issue is with how photos in iOS deals with resizing images.

Such a strange error. Any idea what may be going on here?