If you look at the image in the thumbnail before inserting it, that and obviously inserting it, will tell you how the site is seeing the orientation of your image.
If it's sideways or upside down in the thumbnail, it's going to be that way posted. So just open it in whatever editing tool you use, make a minor change, that's vital, and save.
I just take a pixel off one side, or add at single black pixel inside a dark area, enough to trigger the "revert to original" any Samsung user will know well! You could also pinch zoom and reposition within your frame etc. Or you can resize it to CB size spec instead of the system doing it.
Then save and upload that one. You don't need to rename it.
Any minor change will reset the orientation data and match it to what you see on screen.
That's enough.