The problem with up-side-down and sideways pics is usually to do with your mobile phone and a poorly written computer program.. All phone photos have a digital header which tells computer programs such as this site which way is up. Windows Explorer and no doubt Apple's Explorer(?) use this feature to automatically rotate photos when necessary.
Some web sites and possibly this one don't use the algorithm to automatically rotate photos, thus selfies often end up being inverted. If the above-mentioned trick works, then there's obviously something wrong with the forum script. I discovered that I had to change the theme before my photos would even be accepted, thus the script could obviously do with some coding improvements.
Good luck, or try to remember to invert your phone when taking a selfie.