Need advice: Simple (automatic) way of getting a lightbox effect

I need some advice on how to get a lightbox effect as easy as possible for photos that are uploaded.

The scenario is that I’m setting up a family blog and since some of the family isn’t very “fluent” in how to upload/insert photos I want to make this as simple as possible. Ideally the users should be able to upload a photo, insert it into the post and it would get a lightbox effect without any extra actions.

How can I do this?