Takes a photo from webcam on screen unlock. Works on KDE. Depends on fswebcam, python2, python2-gobject, python2-dbus.

kde-unlock-trigger.py

#!/usr/bin/env python2
# coding: utf-8

COMMAND = 'fswebcam --save ~/Dropbox/images/unlock-{date}.jpeg'

import subprocess
from datetime import datetime

import gobject

import dbus
import dbus.glib

from dbus.mainloop.glib import DBusGMainLoop
dbus.mainloop.glib.DBusGMainLoop(set_as_default=True)

def handler(status):
  if not status:
    cmd = COMMAND.format(date=datetime.now().isoformat())
    subprocess.call(cmd, shell=True)

bus = dbus.SessionBus()
ss = bus.get_object('org.kde.screensaver', '/ScreenSaver')
ss.connect_to_signal("ActiveChanged", handler)

gobject.MainLoop().run()