I have a a webcam which works fine with the uvcvideo driver:

Bus 001 Device 011: ID eb1a:2571 eMPIA Technology, Inc. 

The camera has a small "shot" button on top of it. The button is meant to make instant shots, like on a normal camera.

When I press it, xev shows that the following event is emitted:

KeyPress event, serial 30, synthetic NO, window 0x4a00002,
    root 0x32b, subw 0x0, time 121054805, (742,772), root:(746,832),
    state 0x0, keycode 220 (keysym 0x1008ff8f, XF86WebCam), same_screen YES,
    XLookupString gives 0 bytes: 
    XmbLookupString gives 0 bytes: 
    XFilterEvent returns: False

KeyRelease event, serial 32, synthetic NO, window 0x4a00002,
    root 0x32b, subw 0x0, time 121055029, (763,807), root:(767,867),
    state 0x0, keycode 220 (keysym 0x1008ff8f, XF86WebCam), same_screen YES,
    XLookupString gives 0 bytes: 
    XFilterEvent returns: False

I think 'cheese' must honour this button as an alternative for the "Take a photo" button.

Also, perhaps, GNOME must be set up to launch some webcam app when this button is pressed and no webcam app is running, but that's a different story.