if the device is locked the screenshot of the lock screen will be captured, otherwise it will be a black image. not sure why this happens. might be due to aegis user permissions.
i dont think screenshot is useful for n950. if anybody thinks otherwise, i can try to fix it.

regarding webcam, have u enabled it on the control panel? if so can you post the contents of /var/log/prey2.log, with only webcam enabled on the controlpanel