unpaper is a post-processing tool for scanned sheets of paper, especially for book-pages scanned from previously created photocopies. unpaper tries to remove dark edges, corrects the rotation ("deskew"), and aligns the centering of pages.
Tifftool is a high-performance tool to clean scanned documents in preparation for onscreen display or for OCR. Features include skew correction, orientation correction, despeckle, page alignment, split pages and batch processing.