how can i disable a webcam using windows group policy

Webcam and Microphone

Silverlight allows webpages and applications to access the microphone and webcam. For webpages and sandboxed out of browser applications, Silverlight will display a dialog asking the user's permission to use the microphone/WebCam before allowing the application access to the device. For trusted applications, Silverlight does not display a dialog (however, the application may choose to display its own message).

Silverlight provides settings to disable the use of webcam and microphone. When this setting is disabled, no Silverlight application may access the webcam or microphone, and the dialog asking the user for permission is not shown. This setting is available in the custom ADM or ADMX file you create using the text provided at the bottom of this page. The registry setting for disabling webcam and microphone that the administrative template files contain is:

Key path: HKEY_LOCAL_MACHINE\Software\Microsoft\Silverlight\
Value Name: AllowWebcam
Value Type: DWORD
Valid Values:
    Disabled — 0x00000000
    Enabled — 0x00000001

You can locate this setting in the following policy path for your GPOs:
Category       Description
Computer Configuration\Administrative Templates\Silverlight       Contains settings to enable or disable use of webcam and microphone by Silverlight applications.

From:
http://www.microsoft.com/getsilverlight/resources/documentation/grouppolicysettings.aspx

do you mean i need to install sliverlight on all the desktops/laptops and thenafter apply the policy

Yes.  I couldn't find a way to do it without Silverlight.  if any other expert is aware, please post it.

Can probably use DevCon in a machine startups script....

Just need to disable the classes for Mic/Camera.....

If this seems feasi ble, please let me know and I will work up the commands.....

I did not find solution to my requirment.

Glad you found one....