http://superuser.com/questions/693339/batch-processing-images-of-documents-to-look-like-a-fax/708256

imagemagick-scan-to-mono.sh

#!/usr/bin/env bash
# -*- mode: sh; coding: us-ascii-unix -*-

source libstacktrace || true
set -e -u -E

MANUAL="
Usage: $0 INFILE OUTFILE

Takes a document scan INFILE (an image) and produces a monochromatized
output file version.

"

if [[ "${1:-}" = "-?" ]] || [[ "${1:-}" = "-h" ]] || [[ "${1:-}" = "--help" ]]; then 
    echo "$MANUAL"
    exit 0
fi

BLURRADIUS="20"
INFILE="$(readlink -m "$1")"
OUTFILE="$(readlink -m "$2")"
TMPDIR="$(mktemp -d)"
cd "$TMPDIR"

convert "$INFILE" -colorspace Gray 01.png
convert 01.png -blur "${BLURRADIUS}x${BLURRADIUS}" 02.tif
convert 01.png 02.tif -compose Divide_Src -composite 03.tif 
convert 03.tif -threshold 90% -type bilevel -compress group4 "$OUTFILE"

rm 01.png 02.tif 03.tif
rmdir "$TMPDIR"

# for file in *.jpg; do ./imagemagick-scan-to-mono.sh $file rotated-$file; done