Use Canny Edge Detection for the “good state” template and a difference sample - a door and the cross hatch will have detectable edges, generally no matter the lighting or time of day.
Some video motion detection (optical flow?) can filter out when you “test” for the expected edges - a time-out would reduce false alarms, for example 1-2 minutes (adjustable) of “no motion” in the ROI before testing for the edges should eliminate people standing in your detection zone. You can take a dense optical flow evaluation of the video to create a map of motion in the frame and then also apply Canny Edge Detection to the resultant output of the optical flow process to create some boundaries on moving objects in the video frame - correlation between edges in the original image and edges from the optical flow motion detection give a fairly high probability of that being a solid object - one can then use that resultant solid object for other interesting things like video tripwires, and all kinds of useful things for security/safety purposes.
Item abandoned, item taken, entering or exiting a space (and counting), and on and on.