Gallery, making one with already uploaded images?

Hello everyone,

At the moment I am new to WordPress and I am trying to understand all the basics before I am going to make my own theme(s) and possibly my own plugin(s). So I started readying “WordPress 3 complete” and installed WordPress locally to experiment.

I reached the subject about WordPress gallery’s. Making one isn’t that hard. Upload multiple images and the option for gallery will show up. But now I wondered if its possible to make a gallery from the images you already uploaded (those that you will find back under Media) without using a plugin. This way you wont have duplicate images.