I have not had a chance to test this but was sent an email from a friend that received the email from Walgreens.
Walgreens is offering 20 free 4x6 prints today only when you order online and choose in-store pick up. Go to Walgreens and place your order using code "ONEDAY". Choose in store pick up and you will be able to pick up for free at your local store. The great thing about these deals at Walgreens , is you don't have to pick up on that day. If you finalize the transaction online and make payment(of $0), you can pick up later in the week.