I was wondering if you could use a digital camera that has video on it for a webcam?

It all depends on the camera and connectivity. Many do not. I would just advise you to spend $20 bucks and go out and buy a webcam if you want one.

Some you can..

yeah a lot are meant to do that ... not all though.

I can, but you can't.

It depends on the model.
Look in your documentation to find out or email me with the brand/model number.

Some but not all you should check before buying.