It depends on what you camera supports. The brand I have support RTSP and with that you can use the live stream like this rtsp://84.27.12.000:554/user=admin&password=123456&channel=1&stream=0.sdp?
Note, the url is not for all the camera's the same. Read you manual or google for it.
Bart made a nice example in this topic how to capture 1 frame from the stream;
This works great for me.
And here is a discussion how to overlay text over your image; Overlay text onto image