For the USB camera, you can choose any webcam that is compatible with the UVC protocol. Most of the recent webcams are compatible. I choose a Logitech C270 that can take pictures up to 720p resolution. You can find a list of compatible cameras here:
http://en.wikipedia.org/wiki/List_of_USB_video_class_devices
The first step is to insert the SD card in the Arduino Yun board: