My understanding is that it should be 'double opt-in'. Basically, they first submit their email address, then a confirmation email is sent to them, with a link they need to click to 'confirm' the sign-up.
This prevents people from entering the email addies of their sworn enemies...which I have to admit used to be lots of fun.
If you're requiring them to enter their email address to view your gallery listings, then you wouldn't give them access until after they had clicked the confirmation link.
Now...the wisdom of requiring such a process for your surfers to see the galleries is debatable...and a discussion for another time.