Taking pictures using an external (USB) camera on a Samsung Galaxy S2
I found this: https://play.google.com/store/apps/details?id=infinitegra.trial.usbcamera 
This is an Android application to display and record the video from an USB camera which is connected to a smart phone or a tablet device. For more details please check his website: http://www.infinitegra.co.jp/en/solution/AndroidApp1-spec.htm