watsit said:
Except apparently some browsers don't honor the EXIF rotation data, and the full size image shouldn't be re-encoded with rotation preapplied, making that not viable (unless it can be done losslessly?). Stripping out the EXIF rotation data (to ensure uniform behavior) or refusing uploads with EXIF rotation data (since it would appear wrong for some people) are the only options left.
Since when did we refuse uploads on the basis that they would "appear wrong for some people"?
(Also, for what it's worth, it is possible to losslessly rotate JPEGs by 90 degree angles, although only if the resolution is a multiple of 16 pixels in both dimensions. EDIT: Should clarify I am not suggesting the site should actually do this.)