motion detection, pixels or PIR

I'm using Avtech IP cameras and Security Spy to control them. The motion detection has been unsatisfactory and support at SS tell me they ignore the camera's inbuilt motion detection and all 'motion' detection is based on analysis of pixels in the software.

Can anyone tell me how the camera's inbuilt motion detection actually functions then ? Is it similar to a PIR system or is it also based on variations in pixel illumination ?

The Motion detection is controlled by the recorder, it works on pixelation to pixelation movement so not as accurate as a PIR, you should be able to set areas and sensitivity of motion on your recorder to get it a little more accurate