Rotate Image 90 Degrees

A single 90-degree quarter turn is overwhelmingly the fix for one specific situation: a page scanned or photographed while the source document was fed in sideways, which produces an image that is otherwise correctly oriented apart from being rotated a quarter turn from upright. Flatbed scanners and sheet-fed scanners both produce this fairly often depending on how the paper was loaded, and it is a single consistent rotation rather than something that varies per page, so once you know the correct direction for one page in a batch, the rest usually need the same turn.

Clockwise is the default here because it is the more common case in practice — most scanning orientations that go wrong land the content needing a clockwise correction rather than counterclockwise. If a batch needs the opposite direction, three consecutive 90-degree clockwise turns produce the same result as one counterclockwise turn, since rotation is cyclic every 360 degrees.

When a quarter turn is applied to a batch of scans from the same document, it is worth spot-checking a page from the beginning, middle and end before downloading everything, rather than assuming every page fed through the scanner at the same angle. Multi-page documents scanned in one pass usually are consistent, but a page inserted the wrong way partway through is a common enough exception that a quick check costs far less than re-processing the whole batch afterwards.