Adafruit's article which shows the new process for copying a live SD card PI image to another card with automatic shrinking: https://www.raspberrypi.org/blog/another-update-raspbian/
The nice instructible on the topic that was written before the implementation of the SD card copier: http://www.instructables.com/id/How-to-BackUp-and-Shrink-Your-Raspberry-Pi-Image/