I really need to make an FAQ on this, but by chance, are you uploading photos taken from your phone? If so, here's some information I had provided to somebody else who was also having photo issues that might shed some light:
Many devices don't actually rotate photos when they're taken. Instead, they record the image 'as-is' and then include additional information that tells other devices which way to rotate the picture in order to see it the right way. Unfortunately, they way they do that isn't uniform among different devices or even among different programs on the same device. One of the worst of these is if you use the volume up button like a camera shutter to take a photo on an iPhone, as that actually puts the physical camera in the iPhone upside down. There's more information on this site about it:
The short of it is that you'll have to manually rotate the pictures the right way yourself first if you want to guarantee them to be right side up for everybody. The link above provides some options for this.