Any time you upload a picture to the Gallery, you're automatically subscribed. To unsubscribe, click on 'My stuff' > 'My Subscriptions', and click 'Disable Email Updates' and it will unsubscribe you. You won't know if anyone has commented on them though, unless you go back in and view it manually.
"What, exactly, is the internet? Basically it is a global network exchanging digitized data in such a way that any computer, anywhere, that is equipped with a device called a 'modem', can make a noise like a duck choking on a kazoo." - Dave Barry