the issue you're experiencing is described here:
http://sethfowler.org/blog/2013/09/13/n ... ientation/
firefox implemented a css property that devs can use to make the browser properly orient images like yours.
i've just added it to the forum, so it should show up the right way in desktop firefox now.
unfortunately, i don't think any other desktop browsers have implemented that css property or an equivalent.
on the bright side, i've tweaked the phpBB image resizing plugin i wrote to rotate images like yours so that all browsers will display them properly.
however, if someone uploads an affected image that is sufficiently small, then my plugin won't be triggered (no need to resize an image if it's already small), and in that case it also won't get auto-rotated.
if you want to help test, try uploading that same image again. my plugin should auto-rotate it next time.