Some forums actually do accept externally linked pictures to avoid broken links in case the external hosting site goes down or away. Yacht Forum for instance which is very successful site

As to posting pics upside down I ve never had the issue but since I never post them directly since they have to be resized I am guessing the resize app corrects the upside issue. I am using the Resize It app on my iPhone

And you don’t need to open pics on your computer to rotate them. iOS built in photo app lets you do that