How can I make a screenshot log on Linux?

Question

I wanted to take regular screenshots in Linux every 5 minutes, but with random drift of interval. Just like in this question:

Linux: Take automatic screenshots at random times

but I needed a solution for Arch Linux, which doesn't have cron. I couldn't find a solution for Arch's systemd, so I came up with my own. Additionally, I managed to bypass similar screenshots and generate daily list of screenshots with thumbnails and current window titles in HTML.

Answer 1

This solution uses ImageMagick's compare and import utilities.

As a normal user:

mkdir screenshot-log
vim screenshot.sh
mkdir -p ~/.config/systemd/user
vim ~/.config/systemd/user/screenshot.timer
vim ~/.config/systemd/user/screenshot.service
systemctl --user enable screenshot.timer
systemctl --user daemon-reload
systemctl --user start screenshot.timer
systemctl --user status screenshot.timer
systemctl --user list-timers

screenshot.sh:

#!/usr/bin/bash

DIR="/home/user/screenshot-log"
PREFIX="screenshot"
FORMAT="png"
PNSR_METRIC_DELETE_TRESHOLD=20
HTML_THUMB_WIDTH=200

DATE=`date +%Y-%m-%d__%H_%M_%S`
SCR_NEW="$DIR/$PREFIX-$DATE.$FORMAT"
SCR_LAST=`ls -t $DIR/$PREFIX* | head -1`

# do a screenshot
WINDOW_TITLE=`xdotool getactivewindow getwindowname`
import -window root $SCR_NEW

#requires ImageMagick
DISTANCE=`compare -metric PSNR $SCR_LAST $SCR_NEW /dev/null 2>&1`

if [ "$DISTANCE" = "inf" ]
then
  DISTANCE=1000
fi

IS_SIMILAR=`echo "$DISTANCE > $PNSR_METRIC_DELETE_TRESHOLD" | bc`
if [ "$IS_SIMILAR" = "1" ]
then
  rm $SCR_NEW
#  echo "`date` RM" >> $DIR/log-$PREFIX.log
else
  echo "<p>`date +%H:%M:%S` <a href=\"$SCR_NEW\"><img width=\"$HTML_THUMB_WIDTH\" src=\"$SCR_NEW\" /></a> <br />$WINDOW_TITLE </p>" >> $DIR/`date +%Y-%m-%d`-$PREFIX.html
fi

~/.config/systemd/user/screenshot.timer:

[Unit]
Description=Take screenshot every 5 minutes with random delay

[Timer]
OnCalendar=*:00/5:00
RandomizedDelaySec=3m
AccuracySec=1s
Persistent=false

[Install]
WantedBy=default.target

~/.config/systemd/user/screenshot.service:

[Unit]
Description=Take screenshot
DefaultDependencies=no
After=local-fs.target time-set.target

[Service]
Type=oneshot
ExecStart=/home/user/screenshot.sh