Some. SOME.

If your camera is natively able to then check your settings/manual. If you still can't figure it out post the camera model here.

If there isn't a setting to do it and you try to force it software wise you will break it, as it was not built specifically to take that kind of use.
Most cameras don't have the processes/temporary memory needed to push out images quickly.

I can submit to you several articles that people tell about how if they get a camera to use as a webcam (even when it's made to) it wastes it.

Not only that, but there is no universal program for cameras without the capacity to do it on their own. You would have to write it on your own based on your drivers.