How can I easily make screenshots of screen regions on Arch Linux with i3 WM?

You can use import, part of ImageMagick.

Capture a region

This will change your cursor into a crosshair and when you click and drag to form a box, that box will be saved as ss.png.

import ss.png

Capture whole display

import -window root ss.png

You can also replace the word root with the window id to capture a specific window.

It's been a long time since I'd asked this question and it looks like it's helpful for some of the users. So I provide my own script for making screenshots with xclip and imagemagick packages.

First of all, install the above mentioned dependencies. Then you can do whatever you want with the script below. It supports making a screenshot of a whole screen or a screen region and also it automatically copies a screenshot to a clipboard so you can paste it everywhere (e.i browser or Telegram messenger).

A couple of not so hard to come up with hacks would add a support for capturing specific windows and toggle copying part.

#!/usr/bin/env bash

# screenshots stuff
# TODO: docs

function help_and_exit {
    if [ -n "${1}" ]; then
        echo "${1}"
    fi
    cat <<-EOF
    Usage: scregcp [-h|-s] [<screenshots_base_folder>]

    Take screenshot of a whole screen or a specified region,
    save it to a specified folder (current folder is default)
    and copy it to a clipboard. 

       -h   - print help and exit
       -s   - take a screenshot of a screen region
EOF
    if [ -n "${1}" ]; then
        exit 1
    fi
    exit 0
}

if [ "${1}" == '-h'  ]; then
    help_and_exit
elif [ "${1:0:1}" == '-' ]; then
    if [ "${1}" != '-s' ]; then
        help_and_exit "error: unknown option ${1}"  
    fi
    base_folder="${2}"
else
    base_folder="${1}"
    params="-window root"
fi  

file_path=${base_folder}$( date '+%Y-%m-%d_%H-%M-%S' )_screenshot.png
import ${params} ${file_path}
xclip -selection clipboard -target image/png -i < ${file_path}

And here is my reference shortcuts for an i3wm to make use of this script:

# take a screenshot of a screen region and copy it to a clipboard
bindsym --release Shift+Print exec "scregcp -s /home/ddnomad/pictures/screenshots/"

# take a screenshot of a whole window and copy it to a clipboard
bindsym --release Print exec "scregcp /home/ddnomad/pictures/screenshots/"

Flameshot is a decent alternative.

bindsym Print       exec flameshot full
bindsym Shift+Print exec flameshot gui

You can use option -p /path/to/directory to skip selecting the save directory.