Registration Disabling and Guest Comments

Hello, I've tried looking through all the administration options, but I could not find out how to do this.

I basically want my photo gallery to be view only by the public. So, I would like to disable the registration of new members completely. Meaning I will be the only one able to modify and add new photos, but people can still view them.

Additionally, I don't know if it's possible (I couldn't find any options to do this either) I was wondering if it could be set up so that a guest could comment. Perhaps where the guest puts in their name and then comments on a photo.

I hope that is possible.