Why does my photo appear upside down on the forum but right-side up elsewhere?

Why it happens

The short answer is because your phone was probably upside down when you took the picture. Your phone logs meta-data in the photo indicating which orientation you intended as up.  Unfortunately, this information isn't always transferred correctly when a photo is uploaded or emailed, and further, some systems simply don't know how to read the orientation data. 

How to fix a photo after uploading to the forum

Open your photo in your editing software of choice and use the rotate feature to rotate the photo at least one full revolution, stopping when the orientation appears correct again, then save the photo and upload it to the forum again. Remember, even if it looks right-side up on your device, rotate at least 1 full revolution before resaving. If it starts upside down in your editing app/software then rotate it 1.5 times so it's correctly oriented. This works most of the time. 

If, however, your photo is an exception, a quick hack is to use the Snipping tool in Windows to take a capture of the photo while it is right side up, or take a screenshot in Android or iOS and crop down to the image, then save and upload this new image to the forum.  

How do I avoid this from happening? 

Take your photos with the phone in it’s right-side up position.  In portrait mode, the lens should be at the top of the phone.  In landscape mode, the lens should be at the upper left corner.