I have not personally needed to forcibly scan a document, i.e., print one out, just to sign it, and then scan it in again. I have my trusty signatures.pdf that I scanned in a few years ago with 10 iterations of my signature. I always just screenshot a signature, and use LibreOffice Draw's ability to set a transparent color of an imported image.
But, after reading an interesting Hacker News discussion, I have whipped up a "scanpdf" solution. 99% of this is ripped straight from the author, mrb.
Here is my file ~/bin/scanpdf.sh, with typo/semantic fixes.
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#!/bin/bash
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# from https://news.ycombinator.com/item?id=30024165#30027344
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# Make a pdf look like it was scanned.
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if [ $# -ne 2 ]; then
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echo "Usage: $0 input output" >&2
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exit 1
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fi
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tmp="$1".scanner-look.tmp
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mkdir "$tmp" &&
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# without -flatten some PDF convert to a JPG with a black background
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convert -density 150 "$1" -colorspace Gray -quality 60 -alpha flatten "$tmp"/p_in.jpg &&
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: || exit 1
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# each page is randomly shifted in the X and Y plane.
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# units seem to depend on angle of rotation in ScaleRotateTranslate?
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offset() { echo $(($RANDOM % 1000)); }
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for f in "$tmp"/p_in*jpg; do
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# each page is randomly rotated by [-0.5 .. 0.5[ degrees
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angle=$(python3 -c 'import random; print(random.random()-0.5)')
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x=$(offset)
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y=$(offset)
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convert "$f" \
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-blur 0x0.5 \
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-distort ScaleRotateTranslate "$x,$y $angle" +repage \
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\( +clone +noise Random -fill white -colorize 95% \) \
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-compose darken \
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-composite \
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${f/p_in/p_out}.pdf || exit 1
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done
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# concatenate all the pages to one PDF
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# use "ls -v" to order files correctly (p_out-X.jpg where X is 0 1 2 ... 9 10 11 ...)
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pdftk $(ls -v "$tmp"/p_out*.pdf) cat output "$2" &&
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rm -rf "$tmp"
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Dependencies include pkdftk(1) and ImageMagick. Also important is to make sure the ImageMagick policy had read and write acess to PDFs. Ensure something similar to this logic is in file /etc/ImageMagick-6/policy.xml.
<policy domain="coder" rights="read | write" pattern="PDF" />
References
Weblinks
- FalsiScan: Make it look like a PDF has been hand signed and scanned | Hacker News
- Edouard Klein / falsisign | Gitlab
- linux - ImageMagick security policy 'PDF' blocking conversion - Stack Overflow
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