When a scanned document is slightly rotated anti-clockwise, this causes a problem for OCR because the 2nd half of every line appears before the 1st half of every line. The incorrect order is a disaster for language translations.
The FOSS tool to deskew is unpaper. But it often fails to deskew. There are --pre-rotate and --post-rotate options which you might expect to give some manual control, but strangely you can only rotate by 90°. The unpaper options are not well explained.
What are folks doing in this situation?
I recall from ~20 years ago Windows paperless tools had a deskewing function that was manual. You draw a line under a line of text on the page and that input is used for rotation. It was limited to PDFs but at least it worked. Is there anything like that in the free world?