Full Screen Galleries (full-screen-galleries) free WordPress plugin

Full Screen Galleries creates an automatic full-screen slideshow mode for image galleries in your content. Posts and pages with galleries are automatically transformed into a full-screen browsing mode when you click on an image. Within the slideshow, visitors can see captions and access full-size images. The slideshow allows visitors to easily browse larger versions of your images.

You can see Full Screen Galleries in action here.

For an automated full-screen slideshow of all content on your site, see the Content Slideshow plugin.