Instead of opening images in a new window display them in fullscreen Lightbox for distraction-free user experience.
To configure Lightbox preferences, please navigate to Settings → Media and scroll down the page to the Lightbox section.
In order to completely disable Lightbox, simply deactivate the Lightbox module on the Powerkit settings page.
You don’t have to add any classes to make the lightbox work. If the lightbox isn’t working on your site, make sure that the “Link To” option of the media file/gallery is set to “Media File”.