September 20, 2014 – Here is a great video tutorial on how to make a custom cardback design using Photoshop.
For customization tips and cardback resources, you can find lots of useful information at FFURG.com (Forgotten Force Ultimate Resource Guide).
Click on the PACKAGING tab to find cardback resources.
If the above are too daunting, you can always check out custom cardback samples on Ebay. Here is a series of LEGO cardback samples ($12.99 each) found on Ebay. The colors, artwork and variety are amazing.