No, the idea is to use a part of the image from the webcam as a indicator for the amount of distortion of the image.
Why? When I point my cam to my car. And I select a square around my car to protect the car around sun-down the webcam-images start to get noise in the images which worsens during the night. After sunset the image is distortion free. So when I set the movement indicator at 10% after sunset moveaction starts making images until sunset... Just because the distortion leads to a difference between images of more than 10%
What I want to do is to select another part of the same image, where I don't expect any movement at all. And use that part of the image to calculate the amount of distortion. Simply by comparing the pixels in that part of the image with the previous image, as you do with the detection zone.
Then I want to add the percentage of difference in this "reference zone" to the threshold for movement-detection. So when I set the threshold to 10% and there is 15% of distortion the threshold would move to 25% This way I hope that after midnight moveaction will correct for the webcam-noise.