Linux commandline tool. From the project's website: "unpaper is a post-processing tool for scanned sheets of paper, especially for book pages that have been scanned from previously created photocopies. The main purpose is to make scanned book pages better readable on screen after conversion to PDF. Additionally, unpaper might be useful to enhance the quality of scanned pages before performing Optical character recognition (OCR). Released for Linux, but could perhaps be run on other OSs with the appropriate compiler?" -- For example, it also runs on Mac OS X and cygwin.