Is it possible to use a digital camera as a web cam?

A few do, but I don't know why you would want to use a high resolution compact digital camera as a $40 webcam.

Webcams are usually quite small and fit nicely on the top of your monitor or in the case of notebook computers attach to the top of the monitor. They also come with the necessary software for both streaming video and take stills for emailing images to your friend.

If the bundled software allows you to. Some camcorders can double as webcams too.