DroidCam turns your Android device into a webcam

The app works with a PC client that connects the computer with your phone. Windows and Linux clients are available.

Features:

Chat using “DroidCam Webcam” on your computer, including Sound and Picture.
Completely free with no usage limits or watermarks.
Connect over WiFi or USB*.
Microphone noise cancellation.
Use other (non camera) apps with DroidCam in the background.
Keeps working with the screen off to conserve battery.
IP web camera MJPEG access (access camera via a browser or from another phone/tablet/etc).