Here is the correction of your english, or at least what I understood from it.
You want to save the picture showing the movement as seen through the motion detection window instead of saving the actual picture.
Unfortunately, I don't think it's possible, at least not that I can see in version 0.3.3 of Yawcam.
I could see it having a certain use to determine whether a motion is a false positive or not, but I don't think it would be a feature used by many.
If this were to get implemented, I would use it a few times to determine what causes my false positives although I am pretty sure it comes from the sunlight. (The camera is pointed slightly away from the window, but the change in lighting that it causes false positives.
I would still want to be able to see the actual picture as well so there would have to be 2 pictures saved at the same time.
Al things considered, I'll add it to the suggestion list and leave it up to Malun to decide.