Open the file /etc/lightdm/lightdm.conf
sudo gedit /etc/lightdm/lightdm.conf
Modify the value of the string "autologin-user" with the required user name
Ex:
autologin-user=pedro
Save the file Reboot/ restart
sudo gedit /etc/lightdm/lightdm.conf
autologin-user=pedro
sh -c 'xfce4-screenshooter --fullscreen --save "$HOME/Pictures/Screenshots/Screenshot_$(date +%Y-%m-%d_%H:%M:%S).png"' s...