Just screenshots the monitor that the mouse is on.

monitorshot2.sh

monitors="$(xrandr | grep -o '[0-9]*x[0-9]*[+-][0-9]*[+-][0-9]*')"
# Get the location of the mouse
eval "$(xdotool getmouselocation --shell --prefix mouse_)"

while read -r line; do
    if [[ "$line" =~ ([0-9]+)x([0-9]+)([+-][0-9]+)([+-][0-9]+) ]]; then
        specs="${BASH_REMATCH[0]}"
        width="${BASH_REMATCH[1]}"
        height="${BASH_REMATCH[2]}"
        x="${BASH_REMATCH[3]}"
        y="${BASH_REMATCH[4]}"
        echo "$width * $height + $offset_x + $offset_y"

        if (( $mouse_X >= $x )) && (( $mouse_X <= $x+$width )) \
               && (( $mouse_Y >= $y )) && (( $mouse_Y <= $y+$height )); then
            import -window root -crop "$specs" /tmp/screenshot.png
            break
        fi
    fi
done < <(xrandr)