Really? I have a bunch, but they wouldn't work. Maybe I'm not putting them in the right spot.
Log in and enter them through this link: http://www.snapfish.com/snapfish/jump/campaignName=mycokerewards
You may have to log out and log in again to see them under your account. Once entered they do not expire. Only one code is allowed of each type per account. Go to your account and redeem them through there.