If you are using raspberry Pi camera:

If you have a monitor, and you want to use it:

Here is the full lists of command: https://www.raspberrypi.org/documentation/raspbian/applications/camera.md

Run camera forever as a preview:

raspistill -t 0

take image

raspistill -o image.jpg

Run preview and take photos when enter is pressed

raspistill -t 0 -k -o my_pics%02d.jpg

Take time-lapse picture, one every 10 seconds for 10 minutes (10 minutes = 600000ms), named image_num_001_today.jpg, image_num_002_today.jpg onwards, with the latest picture also available under the name latest.jpg:

raspistill -t 600000 -tl 10000 -o image_num_%03d_today.jpg -l latest.jpg

If you want to use it over wifi (web interface)

We use RPi-Cam-Web-Interface http://elinux.org/RPi-Cam-Web-Interface

If you want to use a USB web camera

Note that the quality and configurability of the camera module is highly superior to a standard USB webcam. https://www.raspberrypi.org/documentation/usage/webcams/

http://www.slblabs.com/2012/09/26/rpi-webcam-stream/