Activate Lightbox or make fullscreen images actual size

I hope someone can help me with this, I’m truly banging my head against the wall and this has to be a simple thing to do.

I’d like to be able to click on the image in the gallery and have it open Lightbox. Either that or set it to use fullscreen, but have a global setting that only opens the image to the actual size of the full size that I’ve uploaded.

On a large monitor, in order to make fullscreen work, I’d need to upload very large images and I really don’t want them available for download like that.

Lightbox would be preferable, I sure hope someone knows the answer to this.

Thanks!

http://wordpress.org/plugins/galleria/