Posted: 04/08/2014 at 19:42
The technical explanation is that some devices add EXIF information to photos and that contains data on the photo's orientation (and possibly your name, address and location!) Unfortunately not all software understands this information so some browsers show it the right way up, some don't. The only guaranteed way to ensure everyone can see it the right way up is to open it in a photo editing application which allows you to remove the EXIF data. Unfortunately there are so many devices out there that I can't provide a list of what to use which will work for everybody, but there are lots of free ways to do it, like this one:
Once the EXIF data has been stripped out, you might still have to rotate your picture if you took it with your i-Thing upside down, but once done it should stay done!