convert -density 150 input.pdf -rotate "$([ $((RANDOM % 2)) -eq 1 ] && echo -)0.$(($RANDOM % 4 + 5))" -attenuate 0.4 +noise Multiplicative -attenuate 0.03 +noise Multiplicative -sharpen 0x1.0 -colorspace Gray output.pdf

https://github.com/googlecreativelab/teachable-machine

also sync support
http://mp4museum.org/howto-sync/

gifsicle -U --disposal=previous --transparent="#ffffff" -O2 anim.gif > anim_trans.gif

History: Bacon cipher

convert in.png -fill white -fuzz 80% +opaque "#000000" out.png

// Dot Gain Settings
Newspapers: 34%
Magazines and brochures: 24%
High-end brochures: 22%
–
// Common Minimum Highlight Settings
Newspapers: 5%
Magazines and brochures: 3%
High-end brochures: 3%
–
// Common Maximum Shadow Settings
Newspapers: 75%
Magazines and brochures: 90%
High-end brochures: 95%