I'll take a shot at an answer..
When you initially load your photos from your camera into your PC / MAC, I'm assuming that some of them may need to be rotated by you, in your photo viewing/editing software, in order for them to look right on your PC / MAC screen.
Then when you upload them here, they look the same way they did when you initially imported them from the camera, even though you fixed them in your photo software.
The issue is that a lot of photo viewing/editing software stores all the changes you make to a picture in a separate hidden file or in a photo database somewhere. The reason they do this is to protect your original image, and also make it so you can come back at a later date and most likely 'undo' a change you had made.
What you need to do is 'export' or 'save' or 'save a copy' of the image file, which should save it with all the changes you have made to a different filename or in a different folder.
Then when you go to upload here, make sure you upload the newly saved/exported copy and you should be all set.
-- Tom