A picture straight out of a camera is not always oriented in the natural view, and some applications will put the occasional landscape page among mostly portrait pages in portrait making it difficult to read.

Say which direction you want to rotate and, if there is more than one page, which pages you want to rotate.

Just as only contributors can upload files in the first place, also only they can rotate page previews.

Some cameras have a gravity sensor which they use to mark the picture with its orientation. We take notice of this when first adding a picture.