Rain, snow, bugs, … yes, they are tricky to not trigger a motion detection. There are many topics about this and here is a post explaining some of this Difference between sensibility and threshold
The basic problem is actually how the cameras are constructed with IR leds around the lens/sensor or juste beside. It´s an easy construction, but the problem is that the IR light is reflected directly back into the lens system and triggers a motion detection. A recommendation is to use a separate IR source placed at a distance from the camera so immediate reflections can be avoided. Alternative test with another Motion Algorithm. Blob detection worked for some users.
Threshold is at which signal level the system is triggered for a motion detection and a recording will start. “0” is for auto calibration to get rid of noise sources. If threshold is set manually a high value means that the change in signal level between two frames must be high to trigger the system.
Trig duration is 10s by default. When a motion is detected and a recording starts and nothing more happens within 10s the recorded video will be 10s + the prebuffer of about 2s long. If another motion is detected 5s after the recording started the total length of the recorded video will be about 5s+10s+prebuffer, so about 17s.
Frame interval is the time between two frames (video images from the camera) that are used for evaluation if there is a change in the camera view that will be detected as a motion and start a recording. If the object of interest is very fast moving frame interval should be set to a low value. If slow moving objects the frame interval can be set to a higher value. Default is 200ms which work in most cases when people are the objects.
Of cause there are more sophisticated systems with correlation techniques and pattern recognition etc. but these system have another price tag.
That´s the manual we have for the moment. In the section for guides & tutorials there are more information.