#!/bin/sh
slurp | grim -g - - | wl-copy
        

slurp lets you draw a rectangle region and returns the starting and ending coordinates ("0,0 425x426"). grim -g - - takes coordinates from STDIN and grabs the image from that region, and then wl-copy copies data from stdin onto the clipboard.

# In sway config:
bindsym $mod+Shift+s exec ~/bin/snippy.sh
        

Then we can just add a keybinding to sway config to execute that shell script.