https://github.com/naelstrof/slop Can also use a utility like this one, which lets you select an area of the screen and output it in a specified format.
$ sudo apt install slop
$ slop
<selects an area on screen>
1719x1403+1080+277$ clipscreen $(slop -F "%x %y %w %h")
NB. The lack of quotes around $() enables wordsplitting to occur.
$ clipscreen $(slop | tr -s "+x" " ")