iOS generated photos include orientation metadata in the photo. Most PC apps ignore this, and not all cameras include the data. So you can port an iPhoto to a PC app, rotate it, the photo looks fine, put it on a web site, and it's right side up. Great! BUT, if you use an iOS device to view the website, the iOS device sees the bit the PC ignores, and voila, your photo displays upside-down. Whaaa????t?
I had this problem with my blog, drove me nuts (short trip). Finally discovered the thing with the orientation metadata, my PC photo app has a utility that strips the orientation data out, so the photo displays as it appears on the blog, regardless of the device accessing the website.