There are a few steps to make this work.
First, you have to get images into LabVIEW from the webcam. Webcams don't present their data in a standard format, so there's no guarantee that anything will work, but there are a couple of tools out there. NI provides supported tools for GigE and other expensive types of cameras. For USB, NI provides NI-IMAQ for USB but support is limited and your device has to work with DirectShow.
If this doesn't work, you'lkl have to try some other tools. Search for "LabVIEW webcam" and a few things come up, like:
http://mindtrove.info/software/labview-webcam-library/
If it doesn't work, it's because your USB camera doesn't conform to one of the "standards."
Once you have the image in LabVIEW, you need to find a method to look for differences in the images. You can do this with the array tools in LabVIEW, but you'll be starting from scratch. A better method is using the Vision Module:
https://www.ni.com/en-us/shop/product/vision-development-module.html
These threads show some ways to use the Vision Module to do motion tracking:
https://forums.ni.com/t5/LabVIEW/Motion-detection/m-p/65505?requireLogin=False
https://forums.ni.com/t5/Machine-Vision/vision-based-motion-detection/m-p/553492?requireLogin=False
Hope that helps!
