We have a referral program on Piwigo.com. The way it works is easy: when a new user subscribes with your referral code, then both of you get an extra month for free.
Each Piwigo.com account gets a referral code as soon as the subscription is confirmed. You can find this code on your screen [Administration > My Account > Referrals]
Where does the new user enters your referral code? on his subscription management screen [Administration > My Account > Subscription]
When the new user confirms his subscription, you receive a notification by email.
Did I forget to say that there was no limit on the number of referred users? It simply means that if you get enough of them you won’t pay any subscription renewal for a very long time! 10 referred users = 10 extra months for free, 20 referred users = 20 extra months for free…