If you want to protect your galleries, you can

• deploy your website behind a web server like Nginx or Apache and configure basic authentication.
• deploy the galleries behind hard-to-guess URLs, like Dropbox shared galleries. The main upside / downside is that anyone with the link can access the gallery.
• deploy to AWS S3 and add an authentication layer, as below.

Private galleries on AWS

AWS S3 itself does not support authentication. However, you can build a fully self-hosted private gallery using S3 + CloudFront + Cognito + Lambda.

The main benefits of this setup are:

• cheaper and faster than a public S3 bucket, as all photos are cached and served at the edge
• scales to very large number of users, who can sign-up and reset their own passwords
• easily configurable to support Google/Facebook single-sign-on

A full walk-through is available at github.com/thumbsup/aws-private-gallery. This should only take about 1 hour to setup, given you have some AWS knowledge and are comfortable with the command-line.