From LQWiki

A webcam is a digital movie camera that is designed to broadcast in real-time over the global Internet, though it can be any movie camera that can send its signal to a computer. Some webcams come with their own web server and DHCP client installed so they can boot up with an IP address and are ready to serve up live images.

If you want to find out if a particular usb webcam works with linux, there's a list at: http://www.qbik.ch/usb/devices/showdevcat.php?id=9

Programs to use with a webcam

• EKIGA
• camorama
• camstream
• gqcam
• vgrabbj

Webcams documented in this wiki

• QuickCam
• A more complete list: http://www.cs.duke.edu/~reynolds/quickcam/